Is it possible to have a loose connection on one of the temp sensors? Possible bad temp sensor. Disconnect 1 at a time and see which is causing it?
Could you please send all your configuration to us at [email protected]? We like to find out from you what was firmware version, what other components on the board? If possible, we could get hold of your setup, so that we can see what is going on? Sorry for the problem, and thanks for letting us know.
You can try this one:
http://www.ebay.com/itm/251179736436
In addition, you can search for MQ9, MQ7, MQ2 sensors.
You are correct, MQ-7 requires to have 1.5V 90 second+/-1S, then 5V 60 seconds +/-1S. You read the sensor out at the low voltage period.
I think you can control the voltage with 1.5V low voltage is always on, then every 90 seconds turn on one TTL output control a relay providing 5V for 60S.
I didn't think the board has a 1.5V output. If it does, where is it?
5V-1.5V = 3.5V. You could just put a 3.6V zener in series with it and run it straight off the 5V line (1.4V is probably close enough), and then as previously offered, a relay (or high-side transistor switching) to give the 5V pulse. Seems pretty trivial to me actually!
What do you mean by trivial?
Four or five lines of code, a transistor, a resistor and a zener.....
It might be trivial for someone whom has experience with building advanced circuits, but for some of us it is not so trivial. I'm a network admin that does home automation for fun. I don't do much board level work so there is a learning curve for me. With respect, trivial it is not from my point of view but I do like to learn.