Hello,

I rang out (with Ohm meter) the keyboard of a Nokia 6010 cellular phone and have found that all the keys appear to be wired up as normally open switches with all of one side of the switches connected to ground. I hooked up a 4N35 opticoupler NPN transistor across one of the switches such that the emitter was connected to ground and the collector was connected to one of keyboard switchs (zero digit key). This effectively put an open collector NPN transistor across the switch. I then activated the 4N35 opticoupler diode by passing 20 Milliamps thru it with a current limiting resistor. The Nokia senses the simulated switch closure from the NPN transistor but I keep getting false triggering of some of the other keys when I use the phone on a call. There is no interference when the phone is not making a call. The wiring across the keyboard switch is only three inches long and I don't suspect it is picking up any EMI. I have looked across the keyboard keys with an oscilloscope and noticed there are some signals, which I can't figure out what is happening.

My question is does anybody on this forum have any experience with Nokia’s 6010 (or simular) keyboards and how they are scanned?


Regards,

Charles Bannister

Nokia 6010 Cellular Phone