This is revision A of my cheap PIC programmer project.

Cheap PIC Programmer (Revision A)

Revision A Introduction

The revision A printed circuit board was sent out for fabrication in mid-February 1999. A number of problems were encountered and documented in the Notes section below.

Revision A Schematic

The revision A schematic is shown below:

The circuit works as follows.

A wall wart transformer provides 24VAC through power jack N1. The 24VAC goes through a power switch SW1, Fuse F1, and full wave diode rectifying bridge made of diodes D1 through D4. An electroylitic capacitor, C1, a variable voltage regulator, VR1, and a tantalum capacitor, C2, provide a 13 volt linear power supply. The output voltage of 13 volts is set by appropriate selection of resistor values R1 and R2. Please note that VR1 runs quite hot, so a heat sink is required. The electrolytic capacitor, C3, 5 volt voltage regulator, VR2 and tantalum capactior, C4, provide a 5 volt power supply. Resistor R5 and LED1 provide a power on indicator.

Signals from the controlling computer's parallel port interface come in on connector N2. The clock signal comes in on pin 1 (STROBE). The data comes in on pin 2 (DATA1). Pin 3 (DATA2) is used to control the tri-state output of buffer U1B. Pin 7 (DATA6) and pin 8 (DATA7) are used respectively control the application of Vss and Vpp to the chip. Resistor R10, transistor Q3, resistor R7, resistor R6 and transistor Q2 provide a 5 volt voltage follower. Resistor R8 and LED1 indicate when Vdd power is applied. Similarly, resistor R11, transistor Q4, resistor R4, resistor R3 and transistor Q1 provide a voltage follower for Vpp. Resistor R9 and LED2 indicate when Vpp power is applied.

Headers J1, J2, J3, J4, and J5 are used to route Vpp, Vdd, Vss, Clock and Data signals to the 40-pin ZIF chip N3. A shorting block is applied to each header to route the correct signal and voltage to the chip being programmed.

Revision A Printed Circuit Board

The revision A PIC programmer printed circuit board has been layed out. The following files are available:

PIC Programmer PCB Artwork Layer: This contains the artwork layer that specifies where the components are to be placed.
PIC Programmer PCB Back Layer: This is the back (solder) side of the board.
PIC Programmer PCB Front Layer: This is the front (component) side of the board.
PIC Programmer PCB Excellon Drill File: This is the drill file for the PCB in industry standard Excellon format.
PIC Programmer PCB RS-274X Back Layer: This is the industry standard RS-274X file that specifies the apertures and line placement for the back layer.
PIC Programmer PCB RS-274X Front Layer: This is the industry standard RS-274X file that specifies the apertures and line placement for the front layer.
PIC Programmer PCB Drill Size File: This is a short file that specifies the drill sizes for the Excellon drill file.
PIC Programmer PCB Parts List File: This is a the parts list file.
PIC Programmer PCB Size and Hole Counts: This is a short file that specifies the board size and hole count.

Revision A Notes

As I build each project, I type notes to myself immediately below. I consult these notes whenever I do another revision of the board:

Move the power jack up .1 inch.
The holes for the power jack cause problems at Alberta Printed Circuits. HobECAD needs to be tweaked to provide better handling of large holes.
The diode holes for D1-D4 need to be enlarged by one.
Move the capacitors over by one so that the heat sink will `cup' them.
The LED's are too close to the ZIF socket. They are also too close together.
The emitter and collector on Q1 and Q3 are swapped. The base is just fine.
The artwork on the PN2222's is upside down.
The copper letters "CLK" and "DATA" are swapped.
The PIC16F8x needs to run CLK to pin 34. The copper lettering (on the mislabeled CLK header) says pin 35 rather than pin 34. The lettering is incorrect, it really does run to pin 34.
There should be a 5V connection to pin 26 of the parallel port to provide power to my parallel port simulator.
The schematic should have little circles on the inputs to the 74LS125 bus drivers. Alternatively, switch over to a 74LS126 and tie the inputs to Vcc. Actually, I should use a 7407 instead.
Pin 1 of the parallel port connector should be made visible in copper lettering.
There is some room between the power jumpers and the 40-pin connector that could be squeezed out.
Think about moving the pins around to match another programmer so that people can use that programmer's software.
Consider using a 10-turn pot to set the program voltage.
Run everything off of the data pins. It is difficult to control the Clock pin sometimes.
Consider little boards with resisters and LED's that emulate the more common PIC's.