Problem with input signals from darlington driver source

[Flint10]

I want to read an input from a darlinton driver source but I am having problems with the output of the darlington not going low enough i.e. down to approx 1 volt and not zero. This is not low enough to trigger my PICAXE - 28X2.

Is there a simple way of converting this 1 volt to 0V?

Any help would be much appreciated.

 

[Technical]

No,but you can treat it as an analogue input and use readadc instead.

 

[MFB]

You could add a standard diode and pull down resistor at the input of the PICAXE. A Low will therefore be 0.3V and a high will be 4.3V, assuming a 5V supply.

 

[premelec]

I'll second that MFB! just a silicon diode in series with the signal should do it - or 2 diodes in series if necessary and don't forget the 10K or so resistor at the PICAXE input to keep it from floating or rectifying various RFI...

 

[Flint10]

Thanks guys for your prompt advice. I have implemented your mods. I thought it might be the outputs from the darlington driver but alas no.

I am trying to interpret digital signals from a midi device which uses a ULN2803A driver. The idea is that when particular notes are detected the Picaxe -28X2 then switches the relevant relays on and off, either singularly or in pairs, triples etc.

I can get it to work on single notes but the problem occurs when multiple notes are detected.

At the moment LED's on the PIC output go on when a note (event) has been read. No relays are fitted yet.

The program seems to work in principle but I have noticed that when 2 or more events are detected they do not always provide the right output condition. I have noticed that if I shorten the program and only detect certain groups of events it seems to work OK. Also , sometimes an outpput LED may light up fleetingly suggesting that the event has been read but the event doesn't latch even though the code say's high B.1( fot instance) .

I initially thought that the PIC speed was the problem so I have fitted a 10Mhz resonator allowing to to run at 40Mhz.

I have tried to follow the manual regarding interrupt routines and think I understand it. I must admit though I do find the hintsetup and setintflags a bit of an headache to understand.

However, I have dioded an hardware interrupt on INT0 to check when any (upto 5) inputs are triggered then gosub to the interrupt routine to read pinsC condition into a variable b2. This is then used in the relevant subroutine to latch the appropraite outputs.

To help you understand the relvant interrupt code is as follows:-

init:

setfreq em40
input B.0 ; INT0 to check for any input event
output A.0 ; set A.0 as output pin
hintsetup %00000001 ; setup hardware interrupt on B.0
setintflags %00000001, %00000001 ; set hardware Int0 to interrupt
let dirsB = %11111110
let dirsA = %000000001

goto mainloop


interrupt: ;check to see if any input is selected
b2 = pinsC ;read pinsC and put in varialbe b2
hint0flag = 0
hintsetup %00000001
setintflags %00000001, %00000001 ; reset hintflags
return

Is it correct or have I missed the point somewhere?

Sorry for the long post, but this problem is really streching my patience..... Any advice/suggestions would be most appreciated.

Cheers,

Alan