Classic PIC programmer

[uzzors2k]

I built this **broken link removed** programmer, but it didn't seem to respond to any input. I found the problem to be a faulty buffer.

The problem is I don't have any spares, can I leave the buffer out and just connect the programmer directly to the parrallel port?

Also, what does a buffer actually do?

 

[Nigel Goodwin]

I built this **broken link removed** programmer, but it didn't seem to respond to any input. I found the problem to be a faulty buffer.

The problem is I don't have any spares, can I leave the buffer out and just connect the programmer directly to the parrallel port?

Also, what does a buffer actually do?

The buffers are open-collector ones, and are ABSOLUTELY ESSENTIAL to the operation of the circuit!.

You could replace each of the five buffers used with an NPN transistor and a base feed resistor, 10K should be fine. Emitter to 0V, collector to output, input to 10K to base.

 

[uzzors2k]

Sounds like I'll have to wait for a replacement then, since I already built it on a PCB, so stuffing an extra 5 transistors on will be tricky. I'll see what I can do though.

I just have to be sure the buffer is dead first;

I measured 1.7 volts on all of the inputs, and 0.02 volts on the outputs, with only supply voltage and ground connected. When a voltage is applied to the inputs, nothing happens at the output end.

Any ideas as to why it died? Most ICs I've used are pretty robust.

 

[Nigel Goodwin]

I can only suggest you check it more carefully, for a start don't connect it to your computer, test it on it's own. Connect your meter to the output pin of one of the buffers, then connect it's input to 5V and then to 0V, and see what the output reads for each.

I'm presuming you've connected the power pins of the buffer?, or it won't be working at all - and it's not very clear on the diagram.

 

[uzzors2k]

My bad, the 7407 needs external pull-up resistors, and a negative input signal. Under those conditions the programmer works fine.

While testing the programmer on my bench there is 0 volts at Vdd and MCLR, unless I ground pin 4 and 5 on the parallel port connector. Then I get 5 volts and 13 volts. RB7 and RB6 are at a constant 5 volts, unless I ground pins 2 and 3 on the parallel port, at which the pins go to 0 volts.

When I connect the programmer to my computer however, nothing happens, and there is no power on any of the pins to the PIC. Not even during the test function in ICprog. Any solutions to fixing the computer side of things? I'm using Windows XP, ICprog and I've tried inverted the outputs.

 

[uzzors2k]

This time I measured the voltages on the parrallel port directly, and they would either go high or low, according to what I set the test signal to in ICprog. So the problem isn't with the programmer or my computer, but in between.

My programmer reguires negative signals, but my parrallel port seems to provide high (5v) or "low" (0.01v) which isn't low enough! So my problem is right there, I should have bought the 7406 instead then....

Is there any other way around that though? I don't feel like ordering 1 component... Also how does everyone else make this programmer work? I've tried two different PCs, but both of them have a low which is actually 0.1-0.01 volts.

 

[Nigel Goodwin]

This time I measured the voltages on the parrallel port directly, and they would either go high or low, according to what I set the test signal to in ICprog. So the problem isn't with the programmer or my computer, but in between.

My programmer reguires negative signals, but my parrallel port seems to provide high (5v) or "low" (0.01v) which isn't low enough! So my problem is right there, I should have bought the 7406 instead then....

Is there any other way around that though? I don't feel like ordering 1 component... Also how does everyone else make this programmer work? I've tried two different PCs, but both of them have a low which is actually 0.1-0.01 volts.

That's perfectly normal, that's all a LOW is, it's not supposed to be zero.

 

[uzzors2k]

Then I have no idea how this pic programmer is supposed to work. The buffers need to be grounded to allow for anything to happen. But at 0.01 volts they aren't grounded. So at a low signal nothing happens, and at a high signal nothing happens! Wtf!??!!

I took the liberty of redesigning the programmer without buffers. Considering most JDM programmers and how little I use the parallel port, I think it won't put much strain on things. I'll tell you how it goes later today when I've modified the original.

 

[Nigel Goodwin]

Then I have no idea how this pic programmer is supposed to work. The buffers need to be grounded to allow for anything to happen. But at 0.01 volts they aren't grounded. So at a low signal nothing happens, and at a high signal nothing happens! Wtf!??!!

You've probably done something wrong, what you're saying doesn't make any sense!.

I took the liberty of redesigning the programmer without buffers. Considering most JDM programmers and how little I use the parallel port, I think it won't put much strain on things. I'll tell you how it goes later today when I've modified the original.

It can't work, you MUST have an open collector buffer feeding the Vpp switch, and the data input.

 

[eng1]

My programmer reguires negative signals, but my parrallel port seems to provide high (5v) or "low" (0.01v) which isn't low enough! So my problem is right there, I should have bought the 7406 instead then....

No negative signals are required by that programmer.
The 7406 buffers can be used, but they don't change positive voltages into negative ones; they perform the logic invert function.

 

[uzzors2k]

Yess!! I got it working, I had the parrallel port connector mirrored, which explains why everything appeared to work. I programmed a simple led blinker, and it works perfectly.

Thanks for all of the help!