# What is the wavelength of an Itron C1S IR LED?

I'm trying to find an appropriate IR Phototransistor for an Itron Centron C1S Meter. But I can't figure out exactly what is the wavelength of the IR transistor used by Itron.

Do meters have standard IR LEDs? Does it really matter, or can I just get any IR Phototransistor like the TCRT5000 (only the IR Phototransistor)?

• I doubt they use a specific wavelength, just a "handshake" of some sort, to key in the device. Otherwise universal remote manufacturers would have a hell of a time. – Daniel B. May 29 '14 at 4:12

## 1 Answer

Measure the voltage drop across the junction. The band gap energy of the diode junction is also the energy of the photons in electron Volts (eV). Find the wavelength with $$\lambda =\frac{hc}{\mbox{E}}=\left( 4.1366\times 10_{eVs}^{-15\; } \right)\times \; \frac{\left( 3\times 10_{\frac{m}{s}}^{8} \right)}{measu\mbox{re}d\; voltage}$$ Multiply by by 1,000,000,000 or use 3x10^17 for nanometers. You can do this with red or green LEDs and a spectroscope to verify.

However, the IR recievers are pretty broad band and just about any will work.

• Thanks for the equation. I don't have a spectroscope,so... the info that the IR receivers are pretty broad is enough for me. thanks. – otmezger May 29 '14 at 15:32