Colonel By Pic Programmer

Introduction:

• This pic programmer is based on the design of the "el cheapo" by Myke Predko in his in his book "Programming and Customizing PICmicro® Microcontrollers", ISBN 0-07-136173-1. The design has been simplified to accommodate the programming of PIC16F84A and PIC16F876 which will be used at this school, however it will program some other 18 pin and 28 pin PIC microcontrollers. The design allowed for the programmer to be build for under $25.00 cdn in electronic parts plus the cost of the printed circuit board and an enclosure. If you wish to make one you'll have to check availability of parts especially the power supply which was purchased as surplus. You could substitute another suitable supply as long as you get a power jack to match.

What the Circuit Does:

• This circuit is used to download hex files from a PC to program PIC16F84A and PIC16F876 microcontrollers.

  Power Supply - The circuit uses a 14.5 - 16 volt AC/DC power supply of at least 250 ma. The type that directly plugs into the wall is recommended.

  Input - The software referenced below run on a PC will take an appropriate hex file and generate serial signals on the parallel port. These serial signals are transferred down a DB-25M to DB-25M cable and enter the circuit at J1.

  Process - To program a PIC16F84A or a PIC16F876 a VDD of 4.5 to 5.5 Volts and a VPP of 12 to 14 Volts is required. This circuit produces both required supplies and applies them to the correct pins at the correct time. The circuit connects the serial data transmission from the PC to the correct ins of the pic for programming.

  Output - A pic programmer is programmed and the program can be verified.

Links to Documentation:

• Schematic Drawing on MultiSim - Note the schematic is correct except U3 socket actually has pins 0.3 inches apart same as U2. This circuit will not simulate.
• Bill of Material
• Printed Circuit Board Drawing
• Software for this programmer can be download from www.myke.com specifically version 077 @ www.myke.com/elch077.zip. No source code was written for this project.

How the Circuit Works:

• To describe how the circuit works refer to the schematic below. (or to the downloadable schematic on MultiSim linked above)

  

• 13.4 Volt Power Supply:
  • D2-D4, J2, U1, C3
  • J2 accepts 14 to 16 Volts AC/DC from the wall transformer. If J2 accepts AC it is rectified by D4 otherwise D4 can act to protect the circuit in case the polarity at J2 is accidentally reversed. D2 has the effect of reducing the potential by 0.7 Volts. C1 filters the ripple out of the rectified AC which is regulated by U1. U1 is rated at 12 Volts so D2 and D3 are used to increase the output by the voltage drop across each. The output from U1 is 12 + 0.7 + 0.7 = 13.4 Volts. C3 is a decoupling capacitor.
• 5 Volt Power Supply
  • R1, C2, D1
  • D1 is a 5.1 Volt Zener which regulates a 5.1 volt supply. R1 limits the current into the circuit and C2 is a decoupling capacitor. This is applied to the Vdd pins of the PIC
• Circuit to Switch the 13.4 Volts to the MCLR (memory clear) pins of the PIC
  • Q1, Q2, R3, R4
  • R3 and R4 Bias Q2. Q1 is switched by the 5 Volt signal from pin 16 of the parallel port which in turn switches Q2. The emitter of Q2 is connected to the MCLR pins of the PIC.
• Strobe
  • Pin 1 of J1 is a strobe (clock) line. Its 5 volt signal is directly connected to the clock input pin of the PIC
• Data Input
  • R2
  • Pin 17 of J1 receives serial data from the PC to program the pic. This passes through R2 to the Data Input/Output pins of the PIC
• Data Output
  • The Data Input/Output pins of the PIC are also connected to pin 13 of J1 so the PC can read data from the PIC to verify programming. Pin 17 through R2 to Pin 13 can be used to check circuit operation and connection.

Reference Information:

• www.myke.com
• "Programming and Customizing PICmicro® Microcontrollers", ISBN 0-07-136173-1
• Microchip website