Show Posts
Pages: [1] 2 3 ... 6
1  Using Arduino / General Electronics / Re: How to sense Thermostat events with Arduino? on: December 29, 2013, 11:53:18 pm
A friend of mine (EE) created this circuit.



I think I'll go with this one since it's the simplest and I'm not sure exactly about how to wire up the optocoupler. I'll send him any feedback I get here
2  Using Arduino / General Electronics / Re: How to sense Thermostat events with Arduino? on: December 28, 2013, 03:18:47 pm
Found a optocoupler solution https://www.adafruit.com/blog/2012/10/04/ask-an-educator-how-can-i-measure-ac-voltage-with-my-arduino/

Right now I'm leaning towards getting 4 of these http://www.digikey.com/product-detail/en/HCPL3700/HCPL3700-ND/401373
3  Using Arduino / General Electronics / Re: How to sense Thermostat events with Arduino? on: December 28, 2013, 03:02:42 pm
Some more digging has revealed a similar post. Seems this guy used the circuit I posted but it's unclear since a schematic is not referenced http://forum.arduino.cc/index.php?topic=20102.15
4  Using Arduino / General Electronics / Re: How to sense Thermostat events with Arduino? on: December 28, 2013, 02:36:40 pm
Is the optocoupler as simple as connecting a thermostat line with a resistor to the AC side. Then do the same on DC side with 5V and current will flow when AC side is on? If so this seems like the ideal solution for me.

@jimboZA Yeah good point about the exposed wire

If I was doing this, my first choice would be to use a current-limiting resistor and an AC input optocoupler like the ones found on this page:
www.vishay.com/docs/83676/sfh620aa.pdf

My second choice would be to use a bridge rectifier to convert the AC to DC, a filter capacitor to filter out the ripple and then a current-limiting resistor feeding a DC input optocoupler. Similar to a power supply circuit.

Third, would be a bridge rectifier with filter capacitor and a voltage divider to drop the 24V DC down to 5V or less.

Sorry, I'd provide a schematic of each example but I currently have enough trouble typing (recent hand injury) and can't draw anything at the moment.




While you probably already know which wires perform each function (just for future reference of others attempting this), let me add that AC voltage will be seen:

Across W and C when the thermostat is calling for heat,
Across W2 and C when calling for auxiliary heat,
Across Y and C when the thermostat is calling for cooling,
And across G and C when the fan switch on the thermostat is set for manual or 'Fan On.'

Monitoring the actual running of the fan cannot be done from the thermostat, as it is also controlled directly from the furnace itself, most likely by directly switching the mains voltage rather than 24V DC.

And Jimbo is right, WAY too much exposed conductor. You should fix that ASAP.

5  Using Arduino / General Electronics / Re: How to sense Thermostat events with Arduino? on: December 28, 2013, 11:39:19 am
Ok, for anyone else interested in this problem, I, found a circuit on ray's hobby that seems like it will work (#option 4) http://rayshobby.net/?p=6002

6  Using Arduino / General Electronics / How to sense Thermostat events with Arduino? on: December 27, 2013, 04:59:10 pm
I would like to interface my thermostat to an Arduino to receive various thermostat events (heat, 2nd stage heat, cool, fan). I understand the thermostat is 24V AC so where I'm stuck is how can I safely interface this with the Arduino (e.g. heat on reads 5 volts). I've done quite a bit of searching but what I find is people are controlling their thermostat. I only want to "listen" to the thermostat events. My plan is to run a separate cable to the thermostat since I don't want to in any way alter or disturb the furnace wiring. I've looked at my thermostat and I have the following contacts: Power Rh, Rc (heat and cool are jumpered), Common (C) , Heat (W), 2nd Stage Heat (W2), Cool (Y), and Fan (G)

7  Using Arduino / Project Guidance / Re: Voltage drop when relay activates and affects analog readings on: December 15, 2013, 12:01:47 pm
I guess I didn't understand that. There are two GND pins on the Arduino, but I thought they were the same circuit. So are you suggesting I should have relay go in one and the sensor use the other? In either case the problem is solved with the genuine Leonardo.
8  Using Arduino / Project Guidance / Re: Voltage drop when relay activates and affects analog readings on: December 15, 2013, 10:50:47 am
Ok, I was using a Leonardo clone. When I swapped with a genuine Leonardo I don't see any noticeable variation. Is it that the clone has a cheaper vreg? What's interesting is over time the readings stabilize, with the clone

BTW, the humidity sensor is a Honeywell HIH-4030 and yes I had a 1 second delay between readings and relay activation.



9  Using Arduino / Project Guidance / Re: Voltage drop when relay activates and affects analog readings on: December 15, 2013, 01:29:20 am
Thanks for suggestions. Ok it's either the usb power, or it just stabilizes somehow over time. I had it plugged into an external 9V PS (and usb for communication) and after several hours there is still some drop with the relay on but it's very subtle. With usb power I'm seeing about a 1.7 %RH swing.

Any idea if the variance is related to my computer usb power or usb power in general? I was hoping to power the project with a usb wall wart. Of course once I plug that in I can't get serial data to see if the problem still exists.

When it's plugged into both barrel plug power and usb I understand it uses external (barrel plug)

I'm going to let it run overnight on usb power and see if it stabilizes
10  Using Arduino / Sensors / HIH-4030/31 Humidity Sensor Example Code/Circuit on: December 14, 2013, 04:08:46 pm
I thought I'd start a new thread since the last one from 2010 is locked (read only) http://forum.arduino.cc/index.php/topic,19961.0.html

I've been playing with a Sparkfun HIH-4030 to use as a humidstat. I see lots of different functions but not sure where the numbers are coming from. I'm using the following formula, directly from the spec sheet https://www.sparkfun.com/datasheets/Sensors/Weather/SEN-09569-HIH-4030-datasheet.pdf

float voltage = (5.0 * analog0) / 1023.0;
float rh = (voltage - 0.958) / 0.03068;

of course this could be rewritten as

float rh = (voltage - 0.958) * 32.5945;

This seems to be working but the RH values are about 2-3 % below what my desktop digital temp/humidity sensors read.
This seems reasonable as each sensor is different and may require calibration. What I have not done is account for temperature.

I put a 100K resistor across VO and GND per the spec recommendation. I also tried some capacitors 10uF on 5V and VO but they did not seem to help much.

I tried the formula on http://bildr.org/2012/11/hih4030-arduino/ and I get about +4% higher than my reference humidity readings.

The current issue I have is the relay I'm using throws off my RH reading

Any ideas on how to get more accuracy and or improvements would be nice
11  Using Arduino / Project Guidance / Voltage drop when relay activates and affects analog readings on: December 14, 2013, 02:57:59 pm
I have a Sparkfun 5V generic relay hooked up to my Leonardo. I'm driving it via a 2N2222A NPN and have a 1N4004 across the relay contacts.

The relay opens and closes fine but when it's open it drops the voltage about 0.05 to 4.92 and throws off my analog reading (humidity sensor).

The relay has a coil resistance of 60 Ohms and I'm powering it from the Arduino 5V. I've tried both usb power and external 9V power but same result. Is there a solution here or do I just add x to the humidity readings when the relay is on and live with it? Thanks

Here are some readings. Note without the relay the readings are very consistent

Relay On
current: 25.97, high: 26.13, low: 25.97
current: 25.97, high: 26.13, low: 25.97
current: 25.97, high: 26.13, low: 25.97
Relay Off
current: 26.28, high: 26.28, low: 25.97
current: 26.28, high: 26.28, low: 25.97
current: 26.13, high: 26.28, low: 25.97
Relay On
current: 26.13, high: 26.28, low: 25.97
current: 26.44, high: 26.44, low: 25.97
current: 26.28, high: 26.44, low: 25.97
Relay Off
current: 26.60, high: 26.60, low: 25.97
current: 26.60, high: 26.60, low: 25.97
current: 26.44, high: 26.60, low: 25.97

Circuit .
12  Community / Exhibition / Gallery / Re: XBee Garage Door Controller on: October 14, 2011, 10:47:39 am
That's interesting.  I do have an air compressor and have used it a few times since the installation.  No issues yet.  Are you using the internal pull ups or do you let the pin float?
13  Community / Exhibition / Gallery / XBee Garage Door Controller on: October 08, 2011, 10:40:31 pm
I just finished a write up on my latest project: a XBee/Arduino Garage Door Controller.  http://rapplogic.blogspot.com/2011/10/xbeegoogle-talk-garage-door.html  I've included all the source code and described how to get it up and running.
14  Using Arduino / Networking, Protocols, and Devices / Re: While we're discussing xbees on: March 12, 2011, 11:23:44 pm
Do you really need commissioning?  The only config setting you need to get two xbees to talk is the pan id:

ID=1AAA

Do a factory restore (RE) first to clear any lingering settings.
15  Using Arduino / Networking, Protocols, and Devices / Re: How to get variable length data from Xbee packet on: March 12, 2011, 10:08:36 pm
You should always use rx.getDataLength() when iterating through the packet.  It will always return the size of the payload.  The offset + 1 is from the droplet code and is used to skip the status byte.  I routinely send packets of up to 80 bytes so shouldn't be a size issue.
Pages: [1] 2 3 ... 6