SHT11 Data Logger Project - Circuit Problem
Bill Chennault
Posts: 1,198
All--
I am trying to transfer a simple breadboarded circuit--which works fine--to a PCB for use in the field. The circuit consists of a BS2 and a Sensiron Temperature/Humidity Sensor. I am powering it via a DC/DC regulator (SCW05A-05) and a 9vdc wall transformer.
The Stamp communicates with my PC via a USB2RS232. I can program the BS2 just fine with the PCB circuit. However, the temperature and humidity are trash. (The code works fine on the breadboard version.)
I must have "designed" or implemented the BS2/DB-9 connectivity wrong. Will you take a look at my schematic and comment on it?
The red connection was suggested by a forum member (thanks!).
EDIT: Hmmm. If I can successfully program the BS2 on the PCB, doesn't that mean the BS2/DB-9 connectivity is correct?
--Bill
I am trying to transfer a simple breadboarded circuit--which works fine--to a PCB for use in the field. The circuit consists of a BS2 and a Sensiron Temperature/Humidity Sensor. I am powering it via a DC/DC regulator (SCW05A-05) and a 9vdc wall transformer.
The Stamp communicates with my PC via a USB2RS232. I can program the BS2 just fine with the PCB circuit. However, the temperature and humidity are trash. (The code works fine on the breadboard version.)
I must have "designed" or implemented the BS2/DB-9 connectivity wrong. Will you take a look at my schematic and comment on it?
The red connection was suggested by a forum member (thanks!).
EDIT: Hmmm. If I can successfully program the BS2 on the PCB, doesn't that mean the BS2/DB-9 connectivity is correct?
--Bill
930 x 530 - 39K
Comments
Have you verified the module connections to the BS2? see attached thumbnail
Have you tried the Sensirion Demo program as a sanity check?
Have you tried swapping your clock and data line pins in the code to see if it was wired incorrectly?
Have you checked the pins on the SHT11 module with a voltmeter to make sure it has Vdd and Vss properly connected?
Have you ohm'd out the clock and data lines between the BS2 and SHT11 as a sanity check? Put your meter leads on the legs of the BS2 and the tops of the pins of the SHT11.
those are my thoughts, you may have done many of these already.
Studying. I will check everything you suggested and report.
I have SHT11 Data (p1) connected to the BS2 via a 220k resistor. That is a slight addition to the drawing you posted. Is that a problem?
Thanks.
--Bill
Q: What do you mean by trashed; what values are you actually getting?
A: See results below.
SHT1x Demo
soT...... 65535
tC....... 615.3º
tF....... 1139.5º
soRH..... 65535
rhLin.... 2623.1%
rhTrue... 471.8%
Q: Have you verified the module connections to the BS2? see attached thumbnail
A: Yes.
Q: Have you tried the Sensirion Demo program as a sanity check?
A: Yes. Results above.
Q: Have you tried swapping your clock and data line pins in the code to see if it was wired incorrectly?
A: See results below.
SHT1x Demo
soT...... 0
tC....... 6513.6º
tF....... 6513.6º
soRH..... 0
rhLin.... 6549.6%
rhTrue... 60.9%
Q: Have you checked the pins on the SHT11 module with a voltmeter to make sure it has Vdd and Vss properly connected?
A: Yes: +4.97vdc between SHT11 p4 and SHT11 p8.
Q: Have you ohm'd out the clock and data lines between the BS2 and SHT11 as a sanity check? Put your meter leads on the legs of the BS2 and the tops of the pins of the SHT11.
A: Clock: ~0.5ohms. Data: ~4.6k ohms. (I am a real novice here.)
Might the SHT11 be defective due to over-heating during soldering? It is unsocketed.
--Bill
Gee. You might have nailed it. I did not use a 220 ohm resistor. I used a 4.7k ohm resistor. Duh.
I'll swap it.
--Bill
That was it! Thank you very much!
I would have never found that incorrect resistor if you had not suggested it.
I will post a picture of the little project.
--Bill
Here is a picture of my temperature and humidity data logger. It will be very useful in my astrophotography efforts. I'll place it in some kind of enclosure and arrange for the SHT11 to have a window to the outside world. I'm thinking about a square tube from the SHT11 through the enclosure.
Thank you for the help!
--Bill
Will the SHT11 have any risk of condensation sitting out all night?
--Bill
1) Sensirion makes the SF1 filter cap for the sensor that provides IP54 rated protection and I used one for my PlungeLogger. Newark carries it for less than $5. Unfortunately, it cannot be used on the Parallax SHT11 module per the Sensirion recommendations, but you can use it mounted into the chassis wall and use the extension tube like you mentioned to assist with air flow. I am uncertain as to how that would affect the readings for accuracy and/or response time.
2) Tracy Allen also uses goretex type material in some of his projects through EMESystems. The picture with the PG7 gland closed up has the material on it. I have a few pieces from him and if I can locate them in my Sensirion stuff, I'd be happy to send some along. These provide the same protection, but are a bit larger so the vent hole in the chassis can be larger which will improve accuracy/response time.
I do have a small batch of PCBs for the new SHT21 from Sensirion as well as a handful of SHT21s and filter caps for it. The SF2 filter cap is rated to IP67, but my current SHT21 PCB was designed before Sensirion released the drawing so it doesn't have the mounting holes. However, there are other ways to make it work.
Thanks to both of you for confirming that the SHT11 must be protected. My "protection" thought was to place a tube from it to the outside of the enclosure and then make sure that the tube window was pointed downwards. Probably a poor idea.
Dr. Allen's pages on this were instructive for me . . . a newb. Andrew, I will PM you.
Response time for me is not-critical. If response time equates to recorded readings per minute, then I perform one per minute with my VB code. The BS2 attempts to read the SHT11 once per second. The VB code just ignores it until roughly a minute passes.
Even accuracy is not too important. The only thing important--from the SHT11 reporting viewpoint--is consistency. If it is 10*F off it doesn't make any difference as long as it ALWAYS 10*F off . . . +/- a couple of degrees.
--Bill