RoadTest: TI HDC1000EVM Sensor Evaluation Module
Author: michaelwylie
Creation date:
Evaluation Type: Independent Products
Did you receive all parts the manufacturer stated would be included in the package?: True
What other parts do you consider comparable to this product?: Sensirion SHT11, Sensirion SHT21, Silicon Labs Si7201, ST HTS221, and Measurement Specialists HTU21D
What were the biggest problems encountered?: Demo software was not performing well. Drivers are not Windows 8 friendly.
Detailed Review:
Everyone seems to be making temperature and relative humidity (T&RH) sensors recently. At one point, if I recall correctly, Sensirion had the market for T&RH sensors. The SHT1X series of T&RH sensors has been a go-to for over 10 years. The downside, though, is the SHT1x series is expensive at over $10 per sensor, even in bulk purchases. I suspect the SHT2x series by Sensirion was created as a low cost alternative of the SHT1x, but it’s still over $4. Table 1 outlines a comparison amongst a selection of T&RH sensors available as of this writing. Examine the table and notice something interesting: three of the sensors are pin compatible.
I remember Sensirion and Measurement Specialties (MS) having pin compatible sensors. Then along came Silicon Labs (SiLabs) with a new, less expensive, and pin compatible alternative. Now, TI has released the HDC1000. It’s very similar in specification to any of the alternatives, but in bulk quantities it’s only $2.2. My only quam: it’s not pin compatible with the above mentioned sensors. I’m sure there is a good argument for not conforming, but it shouldn’t come as a surprise that it isn’t pin compatible.
Table 1: T&RH Sensor Comparisons. Green highlights are pin compatible.
| Vendor | Texas Instruments | Sensirion | Sensirion | Silicon Labs | ST Microelectronics | Measurement Specialties |
|---|---|---|---|---|---|---|
| Model | HDC1000 | SHT11 | SHT21 | Si7021 | HTS221 | HTU21D |
| RH Range | 0 - 100% | 0 - 100% | 0 - 100% | 0 - 100% | 0 - 100% | 0 - 100% |
| T Range | -40 °C - 125 °C | -40 °C - 123.8 °C | -40 °C - 125 °C | -40 °C - 125 °C | -40 °C - 120 °C | -40 °C - 125 °C |
| RH Accuracy | ±3% | ±3% | ±2% | ±3% | 4.5%, 20 to +80°C | ±2% |
| T Accuracy | 0.2°C (5 - 60 °C) | 0.4 °C | 0.3 °C | 0.4 °C (-10 to 85°C) | 0.5 °C,15 to +40°C | 0.3 °C |
| T Resolution | 14 bits | 14 bit | 14 bit | 14 bit | 16 bit | 14 bit |
| RH Resolution | 14 bits | 12 bit | 12 bit | 12 bit | 16 bit | 12 bit |
| Power Dissipation | 4 uW (11 bit, 1sps) | 300 uW (12 bit, 1sps) | 9.36 uW (8 bit 1sps) | ~24 uW (14 bit, 1sps) * | 6 uW? | 2.7 uW (8 bit 1sps) |
| T Response Time | N/A | 30 sec max | 30 sec max | 5 s (mounted) | 15 s | 10 s |
| RH Response Time | 15 sec | 8 sec | 8 sec | 18 s | 10 s | 10 s |
| Price | $2.2/1k | $12.69/300+ | $4.09/800 | $3.87/2500 | $2.41/1000 | $6.86/100 |
The green bolded options are pin compatible.
*estimated from Datasheet parameters.
This was definitely not a fun experience, but it was no fault of TI. As an engineer I really hate Windows 8’s signed driver requirements. Windows 7 warned you that the driver was not signed, but allowed you to install it anyway. Windows 8 just stops the install procedure and you have to reboot the machine in a special mode to install an unsigned driver. It’s rubbish.
I had major issues with the software. I’ll let the numbers speak for themselves:
Figure 1: Snapshot of the EVM software running.
So, at this point it's obvious the software has major issues. It’s slightly infuriating, but I understand the module is not a data logger. The software is only meant to evaluate the sensor, but it still needs a major debugging. Next I ran a test of the sensor. Here is a picture of the test setup:
Figure 2: Test setup for the evaluation module.
I used a heat gun to raise the temperature of the module to about 120 °C. The maximum of the sensor is 125 °C. We can see from the graph in Figure 3 that the sensor recovered well. Interestingly, the sensor still reports a relative humidity when the temperature is above 100 °C. I’ve always wondered why these type of sensors simply don’t include a flag to indicate the temperature is too high for a relative humidity measurement, but I wouldn’t hold that against the manufacturer. Maybe there is a flag and I missed it, or maybe it should be simply understood by the user that relative humidity above 100 °C is bogus.
Figure 3: Sensor Response.
Finally, I put the module into a Raspberry Pi 2 and tried out Doug Wyman’s code for reading from the module. This worked fantastic and the results were great, which allows me to conclude that the sensor is fine and the issues are with the EVM software.
Despite all the trouble I had, I like the sensor. It works and it’s inexpensive. As an engineer I hate that it’s not pin compatible, but from a business perspective I understand why it isn’t. The meters I design all have optional probe accessories for temperature, relative humidity, and pressure. In the future I would consider this sensor, but currently I prefer the pin compatible options. I can definitely see the HDC1000 being attractive for high volume design.
Until next time ...
Top Comments
Great review and excellent table that will be very useful for people. I've had similar troubles with driver signing (particularly with TI drivers). I completely agree that MS should make driver signing…