This PIC programmer is based on the "El Cheapo" PIC programmer presented in Myke Predko's book "Programming and Customizing PICmicro Microcontrollers". It works with the same El Cheapo software that comes with the book.
I think that Myke's book is outstanding and helped me get started with PIC microcontrollers. It is also very helpful that there is a circuit board included with the book to build the El Cheapo programmer.
Although I think the El Cheapo is a very good low cost and simple design, I was unable to get it to work with any of my PCs, even with a 3 ft (1 m) parallel port cable. I found the problem to be in interface with the parallel port, specifically the time delay circuit on pin 14. This could have been caused by anything, most probably the electrical characteristics of the parallel ports on my PCs.
So, if anyone else has had a similar problem, this enahanced version of the El Cheapo may help you.
The circuit presented here is still Myke's basic design, I just enhanced a few features. My enhancements include the power supply and parallel port buffering, allthough at an increased number of parts.
Here's how it works -
I used a 74LS367 hex buffer to drive some of the lines in and out of the parallel port. The time delay circuit on pins 14 and 15 of the parallel port are buffered with the '367. I also buffered pin 16 which eliminated the need for the 2N7000 FET in the original circuit. I replaced the 2N7000 with a 2N2222 since it is being driven by TTL.
I used a LM317 for the 13.5 volt supply, which feeds a 78L05 for the 5 volt supply. Although the original El Cheapo zener diode circuit worked, I though that the 220 Ohm resistor ran a little hot for my tastes.
Here's the schematic for the PIC programmer -
Here's a picture of the PIC programmer -
On the left, the power connector can seen along with the LM317 regulator (in the TO-5 can) and the 78L05. The green LED next to the power connector is just a pilot light. The 74LS367 can be seen on the right above the parallel connector. I installed 14 and 18 pin sockets in this version. Larger sockets could have been installed but I didn't have any on hand when I built the programmer.
(c) Jon Qualey, August 2006
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