JDM programmer question

[otherguy]

I'm just getting started with my first home-made programmer for use in an upcoming project.

I've chosen to give the **broken link removed** programmer a try since i've been able to salvage nearly every part from old electronics and past projects.

Unfortunately I'm unable to source an 8.2v Zener Diode (D6 in linked JDM scematic). I do however have a number of other zeners including a 7.5v and a 9.1v.
Would it be possible to use either of these in place of the suggested 8.2v zener (D6)?

Thanks in advance.
-Jim

 

[eblc1388]

II do however have a number of other zeners including a 7.5v and a 9.1v.
Would it be possible to use either of these in place of the suggested 8.2v zener (D6)?

A silicon diode like 1N4148 drops about 0.65V when current is flowing. So you can easily adds 0.65V to a 7.5V zener by placing a diode in series with it.

Please read comment about JDM in the Sticky of this forum. Before you starts building, please tests the voltages on your serial port pins to common. If you cannot obtain 7.5V reading or higher with either polarity, the JDM design will most probably not work.

 

[otherguy]

thanks for the info, that's great news... cause i have plenty of 4148 diodes.

And yes, my serial port meets the voltage requirements.

Thanks again for your help.

 

[eblc1388]

When you have built the JDM programmer, do not place a PIC into the socket yet. Run IC-Prog or others programming software and set it up using JDM on your computer.

Connects voltmeter across capacitor C3 and C2 in turn.

Select a PIC say 16F877A in the programming software and perform a "read" operation, getting back all 3FFF as your program word values.

You should get +5V across C3 and +13V across C2 if the circuit works. Then you can test with an actual PIC, after changing the PIC selection in software.

 

[otherguy]

thanks for the info. I'll try that later tonight after getting everything set up on my breadboard.

I'll let you know how it goes.
Thanks,
-Jim

 

[otherguy]

ok, looks like everything's functioning, I've got 13v across C2 and -5v across C3. My com port voltages on TxD, DTR and RTS are all negative values (between -10v to -11v).

Is there something else i need to do before using the programmer?

Thanks in advance,
Jim

 

[eblc1388]

ok, looks like everything's functioning, I've got 13v across C2 and -5v across C3. My com port voltages on TxD, DTR and RTS are all negative values (between -10v to -11v).

Is there something else i need to do before using the programmer?

Thanks in advance,
Jim

You should get +V across both C2 and C3. Please measure again, with the black meter lead touching the neg(-ve) connection of C3. Move red lead to C3 positive will give +5V and C2 positive gives +13V, during a PIC "read" operation.

The JDM design has shifted the programmer common 0V rail. It is is not the computer system common anymore but now located at the negative connections of both capacitors.

If voltages fine, then you can place a PIC to test for real.