Raspberry Pi 2/3 Weather Sensor Shield - Review

I would like to thank Element14 and TE for selecting me for this roadtest. The Raspberry Pi 2/3 Weather Sensor Shield (DPP904R000) piqued my interest for a couple of reasons. First is my ongoing interest in evaluating sensor suits. Because more companies are producing their own sensors its becoming increasingly more complex to select a sensor. Adding these sensors to my comparison chart would allow for a better understanding of the offering from TE. As an ongoing project a platform, for easy comparison of the data, has not yet been established. The second reason for wanting to review the Weather Sensor Shield is a weather balloon project that is due to be completed by the time the weather is more favourable.

First impressions - Unboxing (Lack Thereof)
The board arrived in a padded envelope and an anti-static bag. While I often prefer minimal packaging this was very much bare bones. Being accustomed to receiving even single components in large boxes this was very unusual. Without even a small box for protection, keeping the sensors safe is that much more complicated. Another point to note was the lack of any documentation. While most products do not ship with lengthy guides they do at least ship with a getting started guide or link to an online document. In this case there was nothing included to get a new user started.

The packaging the board arrived in, a shipping box from Element14, which contained the padded envelope in which was the anti-static bag 

On the positive side the board is well marked. Each of the four sensors are clearly labeled. The connector orientation is also well marked to ensure correct mounting. Overall it is a simple board with ample space around each sensor to prevent thermal and mechanical interference between sensors.

Each sensor is clearly labeled as is pin #1 on the connector

Test Outline
I had outlined a series of tests for this kit to determine how user friendly it is as well as how it performs against its outlined specifications. Unfortunately, due to some issues that will explained, most of these tests could not be completed before writing this review.

The test procedure I had outlined for DPP904R000 contained approximately 5 individual tests. These ranged from the usual to those definitely not intended for this kit. The tests outlined in the proposal where as such:

1. How easy would it be to use this with another platform 
2. Can we get the calibration data from the PROMs easily and reliably 
3. Does the data from various sensors match up (they each have a temperature sensor) 
4. Can these sensors survive the outdoor environment, in a sheltered but not sealed enclosure 
5. Can the needed calculations be carried out on a microcontroller without overloading the system 
6. What is the true power consumption of these sensors 
7. What is the theoretical maximum altitude that can be measured with the pressure sensor (taking temperature as well as air pressure into account) 

Due to mainly documentation complications only the first two test have been conducted so far. As more progress is made further updates will be added.

Platform Compatibility
Physical Compatibility
The first test was to see if the DPP904R000 is compatible with with other platforms that have a Raspberry Pi connector. The board selected to test this kit with was the MangOH Red from Sierra Wireless.

MangOH Red from Sierra Wireless

This board has a 26 pin instead of a 40 pin, Raspberry Pi connector. Even with this, only two of the six pins used are not supported. These two pins are apparently used by the Raspberry Pi to read a shields ROM chip for identification purposes. Since the ROM is not used with the MangOH Red, it would not be a concern.

The DPP904R000 mounted on the MangOH Red, only 26 of 40 pins make contact

Communication Compatibility
Using terminal commands to test the basic compatibility between the boards was the next step before moving to any of the other tests. This would also be the first time the documentation was consulted in detail. Any product that survives needs good documentation or support. This is where the Raspberry Pi Weather Sensor Shield started to have issues.

i2cdetect shows 0x76 is reserved by the system and that only the TSD305 at 0x1E is detected

 
The first sensor tested was the HUT21D humidity sensor. This sensors has an easy to follow communication structure. Shortly after reading the datasheet humidity data was being reported back. This quick victory gave a positive feeling towards the Raspberry Pi Weather Sensor Shield, sadly this victory was short lived.

The HTU21D humidity sensor with thermal isolation 

The second sensor to be used with the MangOH Red was the TSYS01. The address listed for the TSYS01 temperature sensor is 0x76 and 0x77 depending on whether the CSB is pulled high or low. Since the MangOH Red has a sensor (BMP280) at 0x76 the TSYS01 sensor could not be reached at this address. However, because the TSYS01 can change its I2C address, there was hope. Looking at the schematics it was revealed that TE did not design this option into their board. While cost could have been a factor ($0.03 for the 0𝛀) there are ways around this (Freescale now NXP, is great at giving options without increasing cost). Unfortunately because of this, the TSYS01 is unusable with the MangOH Red. It would later be discovered that in fact the address could not be changed without causing another conflict.

The TSYS01 temperature sensor with multiple layers of thermal isolation 

The next sensor to be checked for compatibility was the TSD305. While even bad hardware can be made to work with great documentation, no hardware can work with no documentation. This was in essence the case with the TSD305. 

The TSD305 contactless temperature sensor 

 
The datasheet lists the address as 0x00. Interestingly Raspbian (which this board is specifically made for) and other Linux distributions, reserve this address and so its not accessible to the userspace. This left this sensor unusable until I was lead to TE’s GitHub repository. Initially I was shown python drivers, while I was working in the terminal and C this was still more promising than the documentation. Looking through the files it became clear the correct address for the TSD305 is 0x1E. Due to receiving this information rather late, no further testing was conducted with this sensor.

Datasheet displaying 0x00 as the sensor address 

The last sensor to be tested was the MS5637 pressure sensor. Following the sequence of steps need to complete a measurement it is unclear what addresses need to be written/read to/from. At issue are the large number of address available write too. Whether reading pressure or temperature data there are 6 different registers that can be written too, each with a different OSR value. Compounding the matter, is the lack of explanation regarding OSR or how it affects the measurements. Choosing one of these at random the data still needs to be read from the ADC. With no mention of one or two ADCs, at first glance is unclear what address each data point should be read from. Through more careful reading it can be inferred that there is in fact only one ADC.

The MS5637 pressure sensor

Once the sequence of events were clarified an attempting to connect with the MS567 was made. The address for the MS5637 is listed as 0x76. As previously noted, this address is already used by the TSYS01. Besides this address not being incompatible with the MangOH Red, its not compatable with the TSYS01 on the same board (DPP904R000 ). With the unclear sequence of steps along with the an incorrect device address, this device’s documentation is the worst of the four sensors on the DPP904R000 .

Datasheet displaying 0x76 as the sensors address 

As mentioned with the TSD305, the driver files do contain usable information. Very disappointingly TE carried over their mistake from the documentation to the repository. While the hex value is listed as 0x77, which is correct, no one checked the binary value copied over to notice it is in fact 0x76.

The define statement for MS5637_ADDR lists the address as 0x77 and 0b1110110 which are not the same value

 
This leads to another issue. Why would TE select address for different sensors to be the same. Regarding the ability to change address the TSYS01 documentation states “Therefore, two TSYS01 can be interfaced in the same I2C bus”. How can this be so, if the application requires a pressure sensor the second address would be consumed by the MS5637. With 124 address available TE selected two separate sensors that could easily be used in the same application to have overlapping addresses.

Easy of Use with Higher Level Code
The sequence of steps needed to conduct a measurement for these sensors are not necessarily very efficient. The HUT21D requires the system to wait for the measurement to complete before receiving a response. During this time there are two options available. The first option is to wait while the HUT21D holds the SCL line low. This prevents anyone else from using the I2C bus. It may also hold up the system depending how the code is implemented. The second option is to poll the HUT21D waiting for an ACK. While this allows others to use the I2C bus it does require the system to poll the sensor. The other three sensors only provide polling as an option to retrieve data. A better and more efficient option would be to implement an interrupt pin. While this could still require polling in some systems, the time needed to do so would be reduced from milliseconds clock cycles.

This may not be an problem in some systems and even more so in the systems that appear to be targeted by TE. However in low power or time critical systems the extra cycles can reduce battery life or the ability to process data ontime. This would lead to a contradiction in the claim to low power yet the need to use more power to execute and retrieve a measurement.

Documentation and GitHub Repository
As previously noted the documentation for these sensors is lacking, some more than others. There is both missing information as well as clearly incorrect information. The biggest issue found working through these datasheets was the with the TSD305. In this case the sensor address was incorrectly listed as 0x00 instead of 0x1E. Other less critical omissions are lack of explanations or clarifications on how the sensors behave. The most noticeable of these is the OSR values in the MS5637 datasheet. Also unclear in this datasheet is the number of ADCs, the relevance is whether or not there are multiple addresses to read from or not. This though can be clarified with a more careful reading of the datasheet.

One thing that that is very helpful and allows a user to achieve the stated accuracy quickly are the worked examples. The datasheets for each sensor has a fully worked example from capturing the ADC value to computing the actual measured value. Even the simplest of sensors, the HUT21D, has simulated input data that is then converted. This gives a user real values to run through the code to check the calculations with.

Possibly the biggest omission in the documentation is the mention of a GitHub repository for these sensors. This repository contains generic C and python drivers. Also in the repository are demos and drivers for Arduino. The complication here appears to be two different product pages for the same product. The page linked from Google as well as some of the vendors does not mention GitHub or IBM BlueMIX. However, another page found does, under “Related Materials”, mention both of these resources. Also at issue is, while these are mentioned in the datasheet for the DPP904R000, it is done so at the bottom where most companies put their copyright and revision information. This means its in a place a decent number of users will not look.

This lack of exposure puts TE’s sensors at a disadvantage over other sensors. While other companies are showing off the drivers for their sensors, TE is not effectively letting users know theirs exist.

Next Steps
Moving forward I am looking to complete my testing with this board. Once completed the data should be available in real time to compare with other sensors in my lab environment. Beyond this is the hope to be able to integrate the sensors (excluding the TSYS01) in the weather balloon project. This would help to determine how reliable they are in such an application as well as how altitude affects them. Included in this is a test to see what is the maximum altitude that the MS5637 can reliably report.

Conclusion
From the limited amount of testing possible with the DPP904R000 it can be said this board is mostly compatible with other platforms. At issue is TE’s decision to not take advantage of the ability to change the I2C addresses where possible. This not only limits its compatibility with the MangOH Red but, potentially with other boards that may be used in conjunction with it. Indeed it is true that this would not help on this board, that is because TE has decided to allocate overlapping addresses to different sensors. Why TE would select address that potentially conflict with their own sensors is baffling at least and self harmful at worst.

The documentation also for the most part does allow for a developer to complete his task. The problem here is the extra time needed to do so due to missing or incorrect information. With a few fixes this could easily and quickly be resolved. Along the same lines is to fix the product pages. Not just the page of the DPP904R000 but of each sensor to include a link to the GitHub and IBM BlueMIX pages.

Once these obstacles are resolved the DPP904R000 would be a great product to work with for most applications. Not included in this category would be time critical and potentially power sensitive applications. The stated accuracy, factory calibration make for a reliable sensor for indoor environmental sensing applications.


Original post on Element14 can be found here

Keysight U1282A Digital Multimeter - Review and IP67 Rating

I would like to thank Element14 and Keysight for selecting me to review the U1282A. Keysight, formerly Agilent Technologies, is a leader in electrical test equipment. While Keysight has been steadily expanding there multimeter offering, the U1282A is the newest in their lineup and first general purpose multimeter to be IP67 rated.

Unboxing and First Impressions

The U1282A comes nicely packaged as most of Keysights multimeters do. The overall presentation when opening the box for the first time is product built to be used hard and to last. The box comes with a built in divider to keep the multimeter separate from the accessories. The leads were neatly tied up in a ziplock bag unfortunately, there was no protection to cover their sharp points. The included test leads appear stiff and at the first chance I had, I swapped them out for a pair that came with my U1272A. Next to the leads was the IR-USB connector to allow for remote data logging as well a firmware upgrades. The inclusion of the IR-USB adapter is a much welcomed decision. As a good deal of problem solving is done over an extended duration being able to record data for that duration is a big help.

Unboxing the Keysight U1282A

Neatly folded on top of both the multimeter and accessories was the “Quick Start Guide” and certificate of calibration. It should be noted that if you ever lose your certificate of calibration and want a copy, Keysight has all the calibration data for each multimeter by serial number.

Reason for Application

I applied for the this road test because of my ongoing work reviewing new products. In this capacity the environments and issues and very wide spread. Some products work in or around water, making the IP67 rating very useful. Other products are supposed to be low power and having a second meter that can perform logging allows for DC power to be easily monitored. Still others are connected to mains power and the ability to quickly determine if the system is live or not can greatly increase the level of safety.

After watching Keysight’s promotional videos demonstrating their IP67 compliance I felt they were weak and unconvincing. Because of this I was very much interested in doing my own real world and maybe slightly exaggerated testing.

 

Another function I was interested in to exploring  was the PWM output. During testing there are times a servo or other PWM controlled device that may appear to not work. Having a known good PWM output can save many hours of troubleshooting. I as therefore curious to see if the PWM from the U1282A could be used as a test PWM for servos.

The last major U1282A function I wanted to evaluate was the Vsense. This function allows you to determine if a wire is live without making an electrical connection. This has the potential to make tasks a lot safer provided it works correctly all the time. Seeing as the number of inline devices or those attached to the mians are also increasing this would help increase the safety during my tests.

I should mention that there was never any intention to look at the accuracy of the U1282A as this is something Keysight is known for. I have only ever heard of one case where a new meter performed incorrect measurements. While this meter did have a calibration certificate this was probably a once of occurrence. I’m also sure that the are others that have reviewed the U1282A and have better means to test the accuracy and repeatability of the meter.

Sand Test

The first issue I wanted to cover was the demo videos from Keysight. As previously mentioned they seemed weak and unconvincing regarding true reliability of the meter. While Keysight did cover the meter is sand there was no attempt to move the selector dial or engage the meter in any mechanical use until after the sand was removed. Also the meter was at one point wetted before covering it with sand trapping the sand on the exteriors of the meter. This has the added benefit of reducing any penetration of sand into the selector dial and the connector terminals.

In the mentioned video the sand was promptly washed off after each time the unit was exposed to sand. In a real world situation we do not get to choose the order the meter is exposed to sand and water or how much of each. Also a bucket of water is most likely not readily available to wash off the sand before the job is completed. Whether it is possible to clean the meter or not, it would still need to be used and function without issue. It should be noted that washing off the meter would render it inoperable until it is dry due to the input warning (leads in wrong input).

In the testing I conducted the meter was completely covered with beach sand. While this may be finer than some sand commonly found, this is with in the size specification for the IP rating. This grain size would also have the potential to be blown around by the wind and into the crevices of the meter making this a valid test. After being subjected to the sand the meter was than cleaned off. This included being brushed off,  washed off with a “hose” as well as rinsed in a bucket. The complete procedure, the meter being covered as well as washed off can be seen in the videos below.

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Immediately it can be heard that here is a decent amount of sand in the dial. Even with the background noise of the water and wind the grinding is unmistakable. The meter was then thoroughly washed off in a bucket of water as well as with a squirt gun.

 

The meter can unmistakably be heard being ground away by the sand stuck between the selector dial and the housing. While it may be considered slightly unfair to operate the selector dial while not completely cleaned from sand, this would most likely be done in a real situation. It should be noted that even with the wind in the background the sound is unmistakable. Also while the Keysight test appeared to show no sand in the dial after being washed off, this was clearly not the case here.

While this may seem like just an annoyance this could conceivably lead to product failure. Specifically this could lead to a breach of the housing allowing water or sand into the housing.This is clearly unacceptable for the IP67 standard, any interference with the satisfactory operation of the unit is considered an issue. The wearing away can be seen in the below picture. In this case the dial was rotated a few times (> 5) producing plastic filings around the AC volts and millivolts section of the dial.

Unfortunately there were only two available solutions to remove the sand. Either send the unit back to Keysight for cleaning or void any calibration warranty and clean the meter myself. Thankfully Keysight took the issue seriously and decided to consider this an “out of the box defect”. In this case the unit was repaired under warranty. I would like to mention that while this issue was being addressed by Keysight internally there was little consensus as to the classification of this issue. The product manager as well as the local FAE appeared to agree that this level of damage to the product should not occur. In contrast the design and test team appeared to be of the opinion that the testing I performed was not valid and the unit behaved as it is designed to and in accordance with the IP67 rating.

“I have checked with the respective team, and we found that it is an expected behavior that the sand may ingress between the rotary switch and the top case. However, the sand will not go inside PCA level of the meter. “

After asking for further clarification due to the grinding of the plastic I received only instructions on how to send the unit back. There was no further information on how the plastic would not be ground down potentially causing a hole in the casing.

Water Test

The water test conducted by Keysight was for the most part sufficient. The meter was submerged and shaken around allowing for water to flow all over the unit. It is true that the meter was not submerged for the required 30 minutes but that was less of a concern considering others have put the meter through that testing. Also with regard to the water tight seals on the unit I don't believe I could do a better test than that conducted by Dave Jones. In his test the meter was submerged, dropped and abused in a very wet and demanding environment. Through all the testing the meter continued to work as designed.

What I have done different than all other water tests to date was to submerge the unit with all input terminals plugged with a test probe. While this would normally not be done and it does sound the input warning alarm, it was done to keep the water out of the terminals. Something I have mentioned to a number of Keysight personal (sales reps, FAEs etc.) is that plugs should be included in the kit or at least be available. The reason is that although the unit is waterproof the input warning will sound until the inputs are fully dry. While the IP67 rating ensures I will not damage my meter if it falls in water or gets wet my testing will be on hold for ~45 minutes or more until the probe terminals are completely dry. Keysight does ship their meters with dust plugs for the test leads and probes, which are sealed when in the field. in contrast to this, there are always at least 2 terminals left open to the elements for dust and water to get in, something is not making sense in this decision.

U1282A with all terminals capped while the meter is submerged

Test and Results

After inserting a lead into each of the 5 terminals the unit was submerged and splashed around a bit. The unit was turned on, the selector switch was rotated. While the unit was on the input warning sounded as expected. Once the water portion was complete the unit was taken out of the bucked and an air hose was used to dry the area around the leads.

When the extra two leads were removed the input warning did not sound. This was tested in all three variations. That is in volts, milliamps and amps mode, in all cases when the leads were inserted correctly the alarm did not sound. This furthers my question why Keysight does not include plugs with the unit for those doing testing in a wet environment.

Customer service

As mentioned above testing the unit in a sandy environment resulted in the selector dial becoming contaminated with grit. Since this was a road test Keysight was looking to keep things as positive as possible. Also because the issue was reported within 30 days of receiving the unit they decided to treat it as an out of box defect.

Unfortunately the process for taking care of this was a little bit convoluted and complex. While I was offered upfront to have the unit repaired I was hoping to get more info on the IP67 rating. This additional information never did come and there is still no clarification on what he unit should or should not be able to handle.

Experience with the return

Part of the reason for such a delay in this review has to do with the repair customer service. The amount of time it took to contact the product manager or anyone that could/would seriously help me was pretty extended. The product manager then needed to contact Malaysia and as well as the design team. Eventually I was informed Keysight would cover all cost in having the unit repaired. I was graciously offered to have the unit picked up from wherever was convenient for me, at home of from the office did not matter. In order to speed up the process I had it picked up from my home as this was closer to the sales representative and would allow for faster pick up.

While the unit was picked up the same day that I was contacted by the local office the whole process in having the unit repaired took substantially longer. I the unit wa shipped back to Malaysia where it was disassembled and cleaned. Then the unit was shipped back to the local office and than to me. In all the process took 6 weeks and 5 days (June 23 - August 9). For a piece of test gear that I would potentially use daily on the job, being without it for almost 7 weeks is unacceptable.

PWM Control (Servo Control)

Having a known valid PWM output is very handy especially when testing parts sent to you for evaluation. As a product tester/evaluator I test various products and devices. One of my recent projects was a robotic hand with 6 DoF. Unfortunately there was an issue with the servos not working as they should. Using the U1282A as a calibrated and valid PWM source made it a simple matter to test whether the issue was the servo or the controller.  

For this setup a 5V supply was connected to the power and ground leads on the servo. The U1282A was connected to the signal line and ground. The servo responded as expected it should with a valid PWM signal. This demonstrated the ease with which a PWM device could be debugged with the meter.

Video of meter controlling servo and scope showing changes of width

Since some servos still demonstrated some issues, the PWM output was connected to a oscilloscope. This again verified that the output appeared to be correct. The U1282A was also connected to a U1272A which has a frequency counter as well as a PWM deconstructor. This outputs the duty cycle as well as the period. Sadly the numbers displayed by the two meters had a significant discrepancy. After mentioning this to Keysight I was informed the U1272A needed a factory reset (not sure how this affects measurements but… ). This sadly did nothing to help remove the discrepancy.

Video of meters showing different numbers

VSense

The last major function of this meter that I was intrigued by was the VSense. This functionality allows you to test if a AC wire is live without needing to make contact. When working with live mains this is a major benefit. From testing inline IoT devices to troubleshooting a water heater this can seriously save you.

Before I got a chance to really test this functionality I found that my water heater was not behaving correctly. As part of the troubleshooting I wanted to be sure the heater was powered. When measuring the voltage between what appeared to be the two terminals a very low voltage was observed (~ 1V). Thankfully before working with anything I tested the circuit with the VSense and found there was still something live. On further inspection only one breaker was fully tripped. The second pole was still connected and was thus allowing something to creep through. I may not be 100% how I measured ~1V while the system was live but I am sure that without VSense things could have gone a lot worse.

I would like to mention that getting the VSense to behave predictably takes some time. When doing some of my further testing I found that there is a need to move the meter around slowly. This is because the sense location does not appear to always register in the same location. Also there are times you will need to change between high sensitivity and low sensitivity to be sure you are measuring the correct wire. Overall though the functionality is very useful and beneficial.

Recording Measurements

Another feature I wanted to look at, indirectly linked to the meter was the ability to log data remotely. Although this is not unique to the U1282A, the U1282A does put an emphasis on data logging. I have used previous iterations of Keysights data logging software with my U1272A with mixed results. While the update was relatively reliable things got worse when trying to log data. There were often times a value or multiple values were missed. Also, in previous iterations only one meter could be used at a time necessitating opening multiple logging windows. Having multiple windows compounded with missing data made the post processing very messy and and difficult to get usable and meaningful data.

In the newest version all these issues appear to have been taken care of. You can now connect to and log from up to 9 meters at the same time. There is also an easy way to either view the history of the data as a graph or as a meter display. The export function also works better than before, giving more options. Like Tektronix, Keysight appears to be realizing that good and easy to use software can be just as important as good hardware.

Keysight PC based remote logging software logging from two meters

The profiles of the connected meters as well as information on how they are connected

Conclusion

Overall this is a solid meter that as most if not all Keysight meters do, delivers good quality and is easy to use. Unfortunately from the IP67 rating as demonstrated by Keysight there is room for improvement or clarification. Most importantly the customer service experience needs a lot of help. Waiting 7 weeks to have a meter repaired is unacceptable.

If someone is looking for a meter that is reliable and delivers sound measurements, than any Keysight meter will do. The chances are someone would be choosing the U1282A for its IP67 rating. In that case I would differentiate between the IP6x and the IPx7. From the testing conducted by Dave Jones on the EEVBlog as well as my own basic testing I would say the U1282A is waterproof without an issue. Any environment that contains moisture or water the U1282A would work well in provided the unused terminals are covered. However, regarding the dust proof rating there are issues. The meter definitely has the ability to fail and the lack of clarification from within Keysight on what the meter should be able to withstand is also an issue. Lastly when the promotional video for Keysights version of IP6x involves covering the unit in sand, there should be no negative effects in doing so.

Based on these conclusions, for a wet environment I would recomend the U1282A but I would like to see Keysight add terminal dust caps to prevent water rendering the unit useless until completely dry. Unfortunately if the intended use is in an environment that contains fine grit sand (beach or desert sand) I don’t belive the U1282A will deliver what Keysight wants you to believe it will.

Update

This is a response from Keysight in relation to the delay I experienced in having the unit serviced: The repair delay you experienced wasn’t representative of typical handheld repair. Normally you’d call in, ship the unit to our local service center, it would be exchanged and you get a new one back. Due to your IP67 questions and concerns, your unit was picked up by me, returned to the factory in Malaysia, analyzed, repaired and returned which was not the normal process.  We took your feedback very serious.

Original post on Element14 can be found here