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Problems with my selfmade programmer

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laplace82

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Hi to all, i'm new in this forum. :D


I built this programmer but i'm not able to program Pics: between pin 4 and pin 8 i only have 6.5V (i should have about 12V) and between pin 1 and pin 8 i have 5V. :(
I used a L7805CV as a voltage regulator.
Any ideas? :chinscrat

Programmer tested on a desktop PC, not a laptop.
 

ravimarcus

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1. Have you checked the voltages without the IC in the programming socket?
2. If the device is bad, it may load your voltage source.
3. Please post a schematic for us to analyze your circuit and help you.

Cheers

Ravi
 

laplace82

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1. yes
3. click in my first post on the words "this programmer" and you'll find the diagram.
 

ravimarcus

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laplace82 said:
1. yes
3. click in my first post on the words "this programmer" and you'll find the diagram.
The culprit could be your PC port driver. The moment a small load is applied, the voltage may drop.

There is a robost ICSP programmer design here. h**p://www.echip.co.in/tools.html

It will cost you less than a dollar to build.

Cheers

Ravi
 

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Hi,
For newbies it is better to have Pic programmers that use a 12/13 V external power supply.
Lots of them are available on the www.
 

laplace82

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the above programmer is a modification of this one that is 100% guaranteed to work.

Why with the 7805 it doesn't work? :?:
 

picnoobie

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In original sch, it uses the USB to supply the circuit with 5v.
with your modification, you are trying to supply the 7805 from the serial port
wich won't work I think. Note that the 7805 requires atleast 7v in it's input to get 5v according to datasheet I got.
 

ravimarcus

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laplace82 said:
the above programmer is a modification of this one that is 100% guaranteed to work.

Why with the 7805 it doesn't work? :?:
picnoobie is right. 7805 or 78L05 needs 7 volts minimum at the input to give 5 volts output. Serial port TX and other lines can provide only about 6 mA (as far as my knowledge goes, check the data sheets of MAX232)

One more thing to be noted. RS232 standard specifies voltages of +/- 3 to +/- 15 volts. Normally all serial ports provide +/- 12V. Some Pc's provide much lower voltage but still meeting the standard.

I recommend not to draw power from the serial ports.

Cheers

Ravi
 

laplace82

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sorry if i don't understood all terms very well but i'm italian.

I measured with a tester the voltage of the seria port (without programmer, empty port) and i have 12V (11.6-1.7 V exactly) from pin 3, 4 and 7.
Theoretically the 7805 has 12V in input...

I have to replace 7805 with the usb cable or there's another solution?
 

picnoobie

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I don't know about sourcing supply from the serial port, but the one I use
works nicely https://feng3.cool.ne.jp/en/pg5v2.html this one don't need optocoupler.
If you don't have usb to power your circuit and you have no other way of supplying your circuit, you can always open your PC and take the red and black wires from unused floppy power connectors (measure, make sure it's the 5v one).
!!WARNING!! do it at your own risk!

Better yet if you have an extra PC Power Supply, search google on how you could use it as benchtop power supply.

good luck!
 

laplace82

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i replace the 7805 with the usb cable and now the programmer works!

Therefore now i'm in trouble in programming a 12F683 with WinPic: programming and verifying the code seems going well but if i make a dump of the code is different (comparison in hex) from the original one.

WinPic needs "particular" settings?
I only setted the programmer as JDM and the kind of device (12f683).

Something about oscillator, vdd before mclr, etc.???
 

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