x10 firecracker + 3 DHT11 = no joy

I have an attic fan controller that utilizes 3 DHT11's and a X10 CM17A firecracker. I have everything hooked up on a protoshield and hooked up to an UNO clone. I know the code is working and the hardware works individually, but with all 3 sensors and the firecracker installed it does not. With 3 sensors installed, the code shows it trying to transmit, but my x10 system does not see the transmission. With 1 sensor installed, the command is received every time.

From what I can discern, the problem appears to be power (or lack there of). I am using a 2A wall wart, so I thought I would be good to go. I am going to try other power cubes to see if that one is faulty, but I don't believe that is the case. Any other thoughts?

Do you poll each DHT11 on a separate pin?

Yes, I have 3 data pins for the 3 DHT11's and 2 more for the CM17A.

Yes, I have 3 data pins for the 3 DHT11’s and 2 more for the CM17A.

I wouldn’t figure for any to be particularly current hungry.
If you monitor 5V with a DVM does it stay up or does it glitch out?
If the 5V glitched the Arduino would reset.

You posted that it’s OK with 1 DHT and the Firecracker, but with 3 DHTs it blows.
So, how does it go with 2 DHTs?

I tested with 0, 1, 2, and 3 hooked up. It appeared to work fine with 0 or 1, but failed with 2 or 3. I am going to do more testing to see if it’s specifically one of the DHT11’s or the quantity. I have some backup modules in case one of these is a dud.

I did not mention this initially, but the DHT11’s are installed at the end of 4 conductor phone wire runs. The documentation said up to 20 meters and they do seem to work fine. Is there any chance that wire length could increase power consumption?

Is there any chance that wire length could increase power consumption?

It will at least affect the signal quality. Never tried with 20 mtr.
What kind of cable is it?

wrt the power, you could use an external power for the DHT's, (keep the GND's connected)

I have only done preliminary testing for a couple minutes, but the voltage seems to stay at a constant 5.08v in all conditions with 0, 1, or 2 DHT11's hooked up. The 3rd DHT11 is in a difficult location to reach, so I'm hoping to leave it alone for now. I have the luxury of owning a XTBM X10 signal meter (forgot I had it when I was doing the original testing). This meter allows me to see what X10 activity is on the power line. Since I'm using the CM17A firecracker to transmit to a CM15A interface (which converts RF to PLC), I can see if/what is received by simply plugging in the XTBM and watching the screen.

I found that with no DHT11's installed and the fan controller on my workbench in the basement, I see the fan on command sent successfully every time. When I plug the DHT11's in, something seems to be happening to the signal such that I see a strange (corrupted?) command.

I've done literally 5 minutes of testing, so I'll do more before I can say for sure what's going on.

It looks like the problem likely lies with the wiring and/or sensor in the attic section that I did not pull. When I installed the controller back in the attic, it once again did not function correctly. As long as the sensor in question was not installed, everything worked fine. I could even install the other DHT11's in the questionable sensor's spot and things worked.

The bad player is installed in the farthest location with the longest wire run AND the unshielded wire is running along side other wires. I assumed that wouldn't be a problem since those cables are shielded (good quality RG6), but that may not be a good assumption. This should be easy to figure out by simply swapping sensors and using that questionable sensor on a different wire. I think I'm really close to figuring this out!

I think I'm really close to figuring this out!

Think you figured it out but only want to have it confirmed :wink: