PICkit2 Compatibile MPLAB Programmer
This is a PICkit 2 MPLAB compatibile Programmer. It is a low-cost development tool with an easy to use interface for programming and debugging Microchip’s Flash families of microcontrollers. The full featured Windows programming interface supports baseline (PIC10F, PIC12F5xx, PIC16F5xx), midrange (PIC12F6xx, PIC16F), PIC18F, PIC24, dsPIC30, dsPIC33, and PIC32 families of 8-bit, 16-bit, and 32-bit microcontrollers, and many Microchip Serial EEPROM products. With Microchip’s powerful MPLAB Integrated Development Environment (IDE) the PICkit 2 enables in-circuit debugging on most PIC microcontrollers. In-Circuit-Debugging runs, halts and single steps the program while the PIC microcontroller is embedded in the application. When halted at a breakpoint, the file registers can be examined and modified.
PICkit2 is a very powerful device, in addition to a PIC-programmer function it can be used as a serial EEPROM programmer or a debugger with certain PICs. Since PICkit2 is a Microchip product they are continuously updating the software and the firmware to support the newer and newer PICs. You can program virtually the entire range of 8 bit MCUs, the 16 bit 24H and dsp series and even the newest 32 bit famliy with PICkit2.
In addition of the above PICkit2 uses USB interface to communicate with the computer, so there's no more pain to use it with modern PCs or laptops with no COM or LPT ports at all. Because Microchip has published the whole schematics and the firmware running in the device we have the chance to rebuild it.
The PICkit2 clone has been designed using only hole-mounted parts as it has less problems to rebuilding. I've also simplified the schematic, so the clone can be built to the same size PCB as the original PICkit2:
* The main difference is that the clone supports 5V power supply only, thats why 3.3V devices will require a small additional board which will be published soon.
* The second change is that I have omitted the two 24C512 EEPROMs that were in the original PICkit2. These are only used for programmer-to-go function, but I think it is absolutely not important capability for a hobbyist.
* The third modification is that MOSFETs are working in the clone instead of bipolar transistors, so minimal additional components are needed. You may find that the Q3 FET switching the power supply towards the target circuit is unnecessarily overrated, however, this allows us to achieve the lowest possible voltage-drop on the power line.
* Finally I've used USB-B connector on the clone. A cable with this type of connector is almost at everybody's hand, or can be bought for some cents. The original miniUSB connector is more expensive and may cause more difficulties to buy.
You can see the schematics on the picture above. All the operations are accomplished by the PIC18F2550. This communicates with the host computer via USB bus, controls the Vpp pump if necessary, switches Vdd and drives the lines to the target circuit. The built-in clock generator uses X1 with C2 and C3 to ensure the correct system clock rate.
L1, Q1, D1, C1 and C4 form a boost DC-DC converter which is controlled by the PIC firmware. The voltage sensing feedback is built from R2 and R3, so the control loop is complete. Q4 and Q5 with R5 are for switching Vpp to the MCLR/Vpp output. Q6 with R4 gives an active pull-down to MCLR line when it is needed. LED1 (green, with R12) shows that the clone consumes power supply from the USB.
R16 and Q3 are for switching the Vdd on the output Vdd line. Vdd sensing feedback to the PIC is worked up with R6. Q2 with R1 and R17 form the active pull-down at the output Vdd line. The D2 (if fitted) only protects the circuit against external voltage from Vdd. Yellow colored LED2 (with its series resistor R11) indicates that Vdd is switched to the output.
The red LED3 (with R10) is controlled by the firmware to indicate different states of operating. Normally it lights during the read and write operations, means "busy" state.
R7, R8 and R9 are current limiting resistors in series the output lines PGD, PGC and AUX. R15 and R14 ensures the low level at the PGD and PGC lines in certain cases.
C5, C6 and C7 are power-line decoupling capacitors while R13 acts as a discharger load after disconnecting the device from USB.
S1 push-button has two functions:
* holding down during connecting PICkit2 to the USB the device starts in a special bootloader mode - in this mode only downloading a new firmware is available from the PICkit2 handling software;
* during normal operation a push can trigger the handling software to reload the last used hex file and program it to the attached device if this is enabled in the software.
The PCB design and fitting picture are shown below. It is one-sided, only some straight wires can be found on the component side (red lines). This makes it easy to print the board at home too. I put a text onto the PCB to make easier to identify the right side of the layout. This is a crucial part that you have to be able to read the text on the copper - so you can double check it before the etching. Layout has been exported from Eagle into PNG format with 600 dpi resolution. A friend of mine had been converted the image to PDF, it looks fine too. The pictures with the original size and Eagle files can be found in the package at the bottom of this page.
You must know that protection diode D2 (BAT85 on schematics) drops much more voltage on Vdd line than the switching FET Q3. If you wish, the voltage drop of the protection diode can be eliminated by shorting the place of it. If you don't want to totally cancelling this protection, you can use a lower drop type, eg. 1N5819.
The PIC is better to build in using a socket. Design around Q3 allows you to replace the Q3 (IRF9Z34) with a significantly cheaper BC640 bipolar transistor (as you can see on my prototype). In this case the output current is limited to a few hundred milliamperes with an acceptable voltage drop.
Otherwise, assembling the board is not a complicated task, although bewaring of the accidental shorts is essential. After populating the PCB up you would check the electrical connections with a buzzer (continuity tester).
Unfortunately to start the clone you have to program the firmware into the 18F2550 - you will need a secondary programmer for this. Once the PICKit2 firmware has been programmed into the 18F2550, you can upgrade it without the need of another programmer, because the firmware also includes a bootloader.
The newest firmware version always can be found at Microchip's site, but the current version is also in the package of this article at our download area - click here to download!
After electrical checks against unwanted short- or open circuits on the PCB wires the board can be attached to a computer. Connecting the clone to the USB, the PC should detect it as a HID compliant device. In a Windows XP system open the device manager and check if it is there. Next, start the handling software "PICkit2" and check the status reported by it. The status should show "PICkit2 connected." text and shouldn't be red backgrounded.
If it seems to be all right, you should click on "troubleshoot" from "tools" menu and follow through the troubleshooting wizard. This procedure requires a voltage meter. Note, that the clone cannot regulate voltage on output Vdd line, so changing it in the PICkit2 program is irrelevant. You should always measure approximately the USB voltage (5V) on the Vdd output when it is turned on.
When you walked through the wizard without any errors you are able to start using your brand new PICkit2 clone, congratulations!
PICkit2 Compatibile MPLAB Programmer