HD-HMI light life

[cdenk]

What is the life of the light on the HD-HMI. I'm thinking that 2- years continuous on, is too long, and I need to switch it on and off as needed. Use one of the Function keys to turn on, and a PLC timer to turn it off utilizing one of the output terminals.

Also has anyone done a dimmer using a photo cell and one of DAC's, but I don't have an ADC available, they are all in use.

[support]

Do you mean the backlight on the MD-HMI? The backlight is LED based so the life is really indefinite just like most LEDs. Make sure that the power resistor for the backlight is installed at a location for it to easily dissipate its heat build up. Failure of the backlight resistor may lead to failure of the backlight if it short circuit (it won't be a big problem if it opens circuit).

Not sure I understand what you mean by dimmer with photo cell. Do you mean that the dimmer will light up if the environment become dimmer? If you want to sense the light level you either need an ADC or build a comparator circuit to turn on/off a digital input. Dimming effect can be controlled by PWM and your software has  full control of how long the dimming or brightening is going to take.

[cdenk]

Yes, I'm talking of the HD-HMI backlight, I didn't know if it was LED or other technology. And for the dimming, yes, was thinking of as you describe with ADC and PWM, but since I don't have an ADC input available (actually there are 11 I'm bringing in, with a multiplex circuit for 4 along with signal conditioning), that would require more electronics, which at this point isn't going to happen. Probably going to use a timer set to say 20 minutes, a function key,  an electronic relay (transistor) to close the circuit to the 12 VDC power and output to the backlight.

Thanks for the as usual prompt reply.