Steering remote questeion / electronics help

[sdoom]

Hi , maybe somebody here can help me finding my fault on the following schematic. It´s an adapter circuit for a Toyota Steering Remote --> Pioneer head unit. The strange thing is that the circuit basically works fine after power has been turned on for 2-3 minutes. In the first 2-3 minutes all functions work fine except for the "seek +" switch. I traced it down a bit and found the LM324 is not activating the most upper channel during the fault time.

If I try to check the voltage on pin 12 or 13 everything looks fine and in that moment the output of the LM324 works fine. Already replaced teh LM324 and the corresponding 4066 (I have been told those often go wrong and cause strange behaviour). So I´m not sure what else I could do .

Thanks

Stephan

[sdoom]

fixed it.

After trying another OpAmp I thought that cant be the problem. I could force the behavior with compressed air spray to coo down the curcuit board.

Raised the output voltage of the LM7805 to a 7806 and now it seems to work fine from the start up.

Any idea why the LM324 behaves like this ?

[Mooly]

Probably because the levels are slightly out to drive the CMOS switch. The LM324 data sheet shows that it can swing to VCC less 1.5 volts and that might not be enough for a 4016/66 on 5 volts.

When faced with any problem like this check the basics. Calculate and work out what the DC voltages are in the resistor chains and confirm those voltages actually appear at the opamp input pins.

If they do move on and check the outputs of the opamp change state from low to high as expected. If that is OK then the check the CMOS switch is operating.

Somewhere in that chain of events something will fail to work... and I think it's down to circuit design not accounting for correct CMOS logic levels that do change with supply voltage.

[sdoom]

Thanks for the info , I missed the 1.5V drop in the LM324 datasheet.

I did actually want to use the lowest voltage available because I dont know what kind of resistors (wattage) are build into the Toyota remote. When the LM324 switched, it actually switched 5 V to the outputs (like I said it was always working for the three other buttons)

My first design used a level - meter chip but that was not accurate enough to seperate the different voltage readings from the remote.

Well it works fine now , all that counts.

[Mooly]

Pleased it all works. Things get interesting designing for low voltages

Although I can't just think of any offhand there are some opamps that will swing rail to rail so it's worth checking data sheets etc.

Excellent job, well done.

[sdoom]

Jep that´s another reason why I picked the LM324 --> had them in the box The whole stuff is basically build from 1-2€ parts. They charge almost 60 € for a remote adapter at ebay and I´d guess that there is not much more "high-tech" used inside those black boxes.

I picked the 4066 because Pioneer used them inside their amplifiers,too . There they even switch analog sound from the RCA inputs to the pre-amps and filters. So I thought the 4066 would be a great part to be on the safe side when connecting it to my head unit.