Resistor tolerances

[ash]

Hi I'm a newbie on the forum.

I'm attempting to make the 8 output led only function decoder.

I have made the strip board circuit and programmed the pic.

The voltages seem correct, but the decoder does not work.

I have have used 5% tolerance resistors as I had plenty in stock, is imperative that 1% resistors are used as I think this may be my problem.

Thanks

Ash

[Paul Harman]

Ash

The resistor tollerances are only important on R1-4, and then only when the incoming track signal is outside the NMRA specification (i.e. on dirty track).

Probably the next thing to test is to connect the track input to DC and check the voltages on pins 12 and 13 - one should be higher than the other, when you reverse the track voltage you should see the voltage change correspondingly on the two pins. One will be about 3V and the other a lot less.

While you are playin with DC, try setting the CVs for some DC configurations and check that it will work OK on DC.

[ash]

Paul

Thanks for your rapid reply

I not had much time to play this evening but I will try what you suggest tomorrow.

Could you please clarify the polarity of diodes D5 and D6 on the DIY decoder 8-output LED only version stripboard layout topside.

regards

Ash

[Paul Harman]

The rectifier diodes have their cathodes (stripe end) to the top of the diagram as shown. Get any one of those wrong and you will have a short circuit that will damage the diodes. If the voltages are all correct you are unlikely to have got them wrong.

[ash]

Thanks once again Paul.

I think I'll start again over the weekend with a soldeless breadboard.


regards


Ash