The PICkit2- programmer, PK2M for short, is yet another clone of the Microchip PICkit2 PIC programmer. The design goal was full featured clone with reduced BOM. The BOM reduction here means smaller number of different part types, not smaller total part count.

Features

• Compatible with original PICkit2, can be used with MPLAB 8.92 or stand-alone software
• 20 different component types used (original PICkit2 uses 33 different component types)
• Supports all the extra features as the original (Programmer-to-go, logic tool and UART tool)
• UART tool baud rate improved to 115200 baud, on short bursts even higher (original PK2 limited to 38400 baud)
• Designed to fit in readily available enclosure
• Flimsy mini-USB replaced with more robust USB B
• Choice of either ICD-style RJ12 or PICkit-style 6-pin socket strip for ICSP connector

Circuit design

The circuit is based on the original PICkit2 circuit, with some minor tweaks. The most important change is the microcontroller. PIC18F2550 is replaced with PIC18F25K50. The K50 is cheaper than the original. It also supports clock sync to USB, which allows to drop the crystal and its capacitors, simplifying the BOM. The obvious downside is that K50 requires different firmware. This isn't a huge problem, since the original PICkit2 firmware hasn't been updated since 2008.

Another change is that all the different MOSFETs and diodes have been replaced with BJTs. For most parts this was simple. But the target power switch with reverse leakage protection required some more thought. It is based on the common ideal diode ciruit, which has been modified to work with PNP instead of PMOS. The total voltage drop from USB VBUS to target Vdd is very similar as with original PK2, for currents up to 200 mA.

The original PK2 used comparator interrupts to realize bit-bang UART. The reason for this was probably that the UART was not thought at all when the hardware was designed. On PK2M, the hardware UART pins are connected in parallel to ICSP pins. The hardware UART allows higher baud rates. The downside is that HW UART pins have CMOS input levels, so they don't work with low Vdd.

Firmware

The firmware is compiled with C18 compiler as the original. Some changes were required to adapt to K50. The UART code is modified to use HW UART, and the UART buffer is increased. VPP feedback divisor difference is handled in firmware. Support for inverted MCLR_TGT signal is added (see Variations).

How to build it

I have gathered shared carts for the components. Here is one for TME, here Mouser and here Digikey. The TME card contains also the enclosure, and includes LED spacers and button with long enough stem. Note that you will need some other PIC programmer to program the PIC18F25K50.

The PK2M circuit board is straightforward to assemble. You need to decide whether you want to put it in enclosure. If you do, it is suggested to use 13 mm spacers for the LEDs, and push button with long stem (total height 17...19 mm from PCB surface). If you use transparent enclosure, the LED spacers are not mandatory.

But the enclosure requires some work. The board is designed to fit Kradex Z24A enclosure, which can be bought from TME. It is available in different colors. The transparent one, as shown below, has model number Z24AP ABS.

This Kradex enclosure is a bit unusual. It comes with two screws for closing the enclosure, but you need to drill the holes yourself! Screws for mounting the PCB are not included with enclosure. Suitable screw is 3x5 mm plastic screw, which is listed in BOM. Holes for connectors are best done with a coping saw.

Software

Because the PK2M is basically just the plain old PICkit2, its support hasn't been updated in Microchip official tools for years. So you can only use it with very old PIC devices using MPLAB. Newer devices can be programmed with third-party or open source alternatives. Debugging is only supported in MPLAB. If you plan to do any serious PIC development, I strongly suggest to get some newer debugger.

• PICkit- is the recommended way to use PK2M programmer. It takes advantage of all features of PK2M.
• PICkit+ should also work with PK2M, although I haven't used it. If you have, please let me know about it.
• pic32prog programs PIC32 microcontrollers with many different tools, including PICkit2 and clones.
• AVRDUDE programs AVR microcontrollers with many different tools, including PICkit2 and clones.
• MPLAB 8.92 is the last version of good old MPLAB
• MPLAB-X IDE supports PICkit2 with old PIC devices, but I can't recommend using this software. Note that MPLAB-X IPE tool doesn't support PICkit2 at all.

Variations

Over the years, people have designed different kinds of simplified PICkit2 clones. You can use pretty much all these circuit variations with PK2M too. These allow to simplify the circuit by leaving out components for features you don't need. Common choices are to leave out EEPROM, which is only needed by Programmer-to-Go feaure. Or to leave out target VDD adjustment, which eliminates the opamp and level shift (clamp) transistors.

The PK2M firmware implements inverted MCLR_TGT signal. This allows to make the simplest PICkit2 clone yet, with only 3 components. Because it eliminates also the VPP generator, it only allows LVP (Low Voltage Programming). So in a way, it is like 'PICkit2 SNAP'. But it could be useful if you want to integrate it into a bigger design, where it is needed only for a specific use (e.g. programming a PIC in a production test jig). If you don't need the UART tool, you can omit the connections to pins 17 and 18. For added protection, you could add 100 ohm resistors to MCLR, PGD, PGC and LVP lines.

For more details, see the project web page at kair.us/projects/pk2m_programmer/