Electronic – arduino – Long range sensor readings in a star network with Arduino

1. Output voltage pec is 750mV @ 25'C nom and your reading is what from cold start to after a few minutes? Does it change?

2. Spec is 1000 pF load max you are using twisted cable which is typically 5 pF/cm depending on tpi, diam. etc., so 50cm x 5 = 250 pF, so cable seems ok to prevent instability and oscillation. If you don't have a microamp analog meter get one or use series drop R to estimate.

3. Self heating from 5V should be less < 0.05'C unless it is damaged so measure current against spec to ensure self-heating is not the issue.

4. open air thermal time constant is < 1 minute.. immersed in ice water is 3 seconds . what are the calibration results you get?

5. Do you have 0.1 µF cap across IC?
6. Did you add an op amp to compensate for offset only inherent to TP36 and not TMP35 or TMP37? VOUT @ 1mV/°F – 58°F It is designed for 'F

Step back a few layers and go back to your original problem, which is to count pulses emitted by a LED and be able to access the count information on a PC.

Apparently you get one pulse for every 10 W-h of electricity usage. Even if you were using 10 kW (that's a lot for a house), you'd get one pulse every 3.6 seconds. No problem there. However, you have to determine how long these pulses last. That will determine how sensitive to make the circuit and allow for some noise reduction.

I'd start with a light sensor, suitably condition the light level signal to feed it into a microcontroller, then most of the rest is firmware. Let's say you determine the pulses are 1/4 second (250 ms) long. I'd probably sample the light sensor every 1 ms in the micro, then do a little filtering looking for a square pulse of the expected duration. Even just a threshold detect based on recent ambient with a little hystersis is probably good enough.

Anyway, you get a signal inside the micro for every pulse. Have that increment a counter. You then need to send the counter value to the PC on demand somehow. The simplest was is to use serial. Use something like a MAX-232 chip to convert between the micro's UART and the PC COM port.

I don't see any point in using a 1-wire bus anywhere in this system. There is simply no need for one, and the PC can't speak 1-wire natively anyway.

There is certainly no reason to use a relay anywhere here. A relay will cause glitches, take significant power, and its output will bounce. You don't need isolation because you are only intercepting light from the power meter, which in effect gives you optical isolation from the power line.