Interfacing the Imp with RHT-03 (OneWire support) and IR Goodness

tldstyl3 · December 25, 2014, 5:47pm

Hey,

Sorry to bring this thread out of the dead and happy holidays!

I’m wondering if anybody’s been able to get the RHT-03 working with the Imp since I saw an Imp library for the DHT11 and they seem visually identical…?

I don’t really know what the difference between the two sensors is so I’d really appreciate some info from anyone who can help out.

Thanks in advance!

p.s. I just saw a page which stated that the RHT-03 is also known as DHT22. There’s even some example code detailing how to get it working with RPi - http://davidjkaleta.com/?page_id=26

p.s. 2 Here’s a link to Adafruit with some more info on the difference between the two sensors - https://learn.adafruit.com/dht

Also, here’s the Github link to the Imp library I found on the Imp website - https://github.com/electricimp/reference/tree/master/hardware/DHT22

Can anybody confirm whether they were able to get an RHT-03 (DHT22) working with the above library?

Thanks!

tldstyl3 · December 25, 2014, 6:58pm

Hey, guys!

I went ahead and did a little test to see whether the library would work with my RHT-03 first-hand, but no joy

I’ve attached an image showing my current breadboard config - I believe it’s as instructed by the Github page here:

Sadly, all I’m getting in the log is -

2014-12-26 01:49:24 UTC+2 [Device] Running 138d21b - release-30.22 - Fri Oct 17 12:15:01 2014, Free Memory: 81808 2014-12-26 01:49:24 UTC+2 [Device] Relative Humidity: 0.0 % 2014-12-26 01:49:24 UTC+2 [Device] Temperature: 0.0 C

Any ideas?

gsunada · December 25, 2014, 8:17pm

Your resistor is between pins 1 and 7, not 2 and 7.

tldstyl3 · December 26, 2014, 4:30am

@gsunada - Hey and thanks for trying to help out!

Sadly, the resistor is not the issue - here’s another slightly different angle of the same setup.

Any other ideas? Has anybody actually tried to do this?

Thanks!

Chrischi · December 26, 2014, 1:43pm

I’am using this since months…

send me your SC and i can test it with my setup.

but first change the timmings for RHT-03’s

Zero 30
One 75

tldstyl3 · December 26, 2014, 4:44pm

Hey, @Chrischi

I pretty much just dumped the code from the Github repo found here:

github.com

electricimp/reference/blob/master/hardware/DHT22/dht22.device.nut

// Copyright (c) 2014 Electric Imp
// This file is licensed under the MIT License
// http://opensource.org/licenses/MIT
// Class for DHT22 Temp/Humidity Sensor

const SPICLK = 937.5;
const INTERVAL = 5; // time between readings in seconds

// Class to read the DHT11/DHT22 family of temperature/humidity sensors
// See http://akizukidenshi.com/download/ds/aosong/DHT11.pdf
// These sensors us a proprietary one-wire protocol. The imp
// emulates this protocol with SPI. 
// To use:
//  - tie MOSI to MISO with a 10k resistor
//  - tie MISO to the data line on the sensor
class DHT22 {
    static STARTTIME_LOW     = 0.020000;    // 20 ms low time for start
    static STARTTIME_HIGH    = 0.000020;  // 20 us min high time for start
    static STARTTIME_SENSOR  = 0.000080;  // 80 us low / 80 us high "ACK" from sensor on START
    static MARKTIME          = 0.000050;  // 50 us low pulse between 0 or 1 marks

This file has been truncated. show original

I also tried changing

static ZERO = 0.000026; // 26 us high for "0"

to

static ZERO = 0.000030; // 30 us high for "0"

as you suggested, but I’m still getting

2014-12-26 23:43:27 UTC+2 [Device] Running 138d21b - release-30.22 - Fri Oct 17 12:15:01 2014, Free Memory: 79868 2014-12-26 23:43:27 UTC+2 [Device] Relative Humidity: 0.0 % 2014-12-26 23:43:27 UTC+2 [Device] Temperature: 0.0 C

Any ideas?

tldstyl3 · December 28, 2014, 3:23pm

Hey,

@Hugo - can you please lend your opinion on this matter? The class I’m trying to use is listed on the official drivers list

https://electricimp.com/docs/examples/drivers/

but isn’t working for me despite numerous attempts and help from @Chrischi

Has anyone previously reported issues with this driver? How can I troubleshoot this?

Thanks in advance!

osherl · December 28, 2014, 4:57pm

Just to confirm the issue, I also tried with a DHT22 and getting the same 0.0 results.

hugo · December 28, 2014, 11:13pm

I’m afraid I can’t help here. I didn’t write that driver; they aren’t “official drivers”, just drivers written by engineers here and released under an MIT license. Had a quick look around the lab and couldn’t see any maxdetect parts to try it myself either.

Seems like chrischi has no issues here; are you sure the sensor isn’t dead?

tldstyl3 · December 29, 2014, 7:05am

Hey @Hugo and thanks for chiming in!

I’m pretty sure the sensor is fine since it works when hooked up to an Arduino and also @osherl confirmed that he’s seeing the exact same issue as me.

How can we go about troubleshooting this since I really love the Imp platform and have been wanting to implement this sensor into my project for nearly two years now…

Thanks in advance!

Happy holidays!

hugo · December 29, 2014, 2:17pm

Got a scope to look at the waveform being generated? That’d be the first thing I’d look at.

You could obviously pick another sensor. These days there are really cost-effective I2C interfaces temp/humid sensors, eg the new Silicon Labs ones.

http://www.digikey.com/product-detail/en/SI7020-A10-GMR/336-2540-1-ND/4211751

…is $3.50, one-off. More accurate than the maxdetect too.

Chrischi · December 29, 2014, 3:00pm

I used a new IMP001 and just C&P the Class from GitHub.

tied Mosi to Miso with 1k and Miso to Data.

Looks good to me…

2014-12-29 20:56:52 UTC+1 [Device] Running 138d21b - release-30.22 - Fri Oct 17 12:15:01 2014, Free Memory: 81976 2014-12-29 20:56:52 UTC+1 [Device] Relative Humidity: 24.0 % 2014-12-29 20:56:52 UTC+1 [Device] Temperature: 21.0 C

tldstyl3 · December 29, 2014, 7:39pm

Hey,

Thank you very much for the replies!

@Hugo - sadly, I don’t have a Scope on hand (and I probably wouldn’t be able to find the specific issue, even if I did).

If all else fails, I can always try another sensor, as suggested - do you know off the top of your head a drop-in replacement for the DHT22? I’m referring to the following:

Breadboard-friendly - perhaps someone has developed a breakout board? I’d really prefer not to go SMD for this project
No external components
Similar price range
Ideally carried by SparkFun since it’s one of the few overseas companies I can get parts from

@Chrischi - that’s very strange. Myself and @osherl seem to be having issues with the exact same code & sensor which is working for you… Must be something else.

Thanks for the effort, guys!

hugo · December 29, 2014, 7:50pm

HTU21D I2C sensor on a breakout: https://www.sparkfun.com/products/12064 … $15 (vs $10 for the maxdetect part)

3% RH and 0.4C accuracy.

Chrischi · December 30, 2014, 4:38am

+1, i own also the HTU21D I2C sensor and it’s much better than the DHT stuff.

@tldstyl3

you should try to change the code to see the raw communication.
where are you from?

tldstyl3 · December 30, 2014, 7:21pm

Hey,

Thanks for the replies! Too bad these sensors always seem to be a pain when trying to interface with various mCs. Perhaps, I’ll get an HTU21D as suggested and just forget about getting the DHTs working with the Imp for the time being…

@Chrischi - I’m writing in from Bulgaria.

Happy holidays!

miklosbiro · January 14, 2015, 12:41pm

Hi,

I’m having the same issues with the DHT22. Is there well tested budget temp/humidity sensor out there that reportedly has no issues?

thanks

hugo · January 14, 2015, 2:39pm

Yep, see above. HTU21D.

tldstyl3 · January 14, 2015, 5:21pm

Hey @Hugo

My HTU21D shipment should be coming in within a week or so and I was wondering whether there’s a class already written for it?

I checked the official docs, but couldn’t find a link. Can you recall whether you’ve seen anything along those lines off the top of your head?

Thanks in advance!

hugo · January 14, 2015, 6:05pm

No class, no, but it’s pretty simple to use. Appears to be code-compatible with the SHT21 from sensirion that I posted some code for here:

https://discourse.electricimp.com/discussion/500/sht21-need-help/p1