My Tait Serial programmer works alright, but not every computer has a
parallel port, and these days they're almost extinct. Most laptop don't
even have a serial port! Thinking ahead a USB programmer seems like a
smart investment. Fortunately someone has made a diy version, the Brenner8.
It consists of a PIC18F2550 and some transistors, nothing more.
The PIC18F2550 even runs a boost-converter supplying the MCLR
voltage, so all power is supplied through USB! Very elegant. There are
several variations to the main design, but I chose the mini ICSP
version. Since I only program 18 pin PICs the whole 40 pin ZIF socket
would be overkill, and additional sockets can be added to the ICSP connector
The programmer is pretty easy to put together, the catch is the
PIC18F2550 which needs to be programmed with a bootloader. Any parallel or serial port
programmer can do this, I used my previous PIC programmer and this programming software.
Remember to invert VDD and VPP, and that the PIC18F2550 MCLR voltage is
12.5V maximum compared 13.6V used in the Tait programmer. I had to use
a 15k pull down on PGM (pin 26) and a 100 ohm resistor in series
with PGD (pin 28) + 100pF cap to ground on PGD line. PGC is pin 27,
MCLR pin 1, Vdd is pin 20 and ground is pins 8 and 19. The
bootloader hex is bootloader_0_20mhz.hex if using a 20 MHz clock
which we are. All the software and firmware required can be found in USBurn 1.5. Download and install it. Updated firmware and bootloader software can be found at the creator's website.
Once the PIC18F2550 is programmed, build the circuit as shown above. I
had problems with transistors Q2 and Q3, but using BD139's instead
solved it. Q2's base resistor had to be changed to 2.7k. Component
values are fairly non-critical, except for R4, R5, Q1 and D3.
However R4, R5, and D3 can be compensated for in the USBurn
software. Once built, put the programmed PIC18F2550 into the programmer
and plug it in. The computer should recognize the device, and prompt
you to install drivers. Click through until you can select a location
to install the the drivers from, then browse to the drivers folder in
the USBurn folder. Select it and windows should install the drivers.
Once installed, go to control panel -> system -> hardware ->
device manager -> other devices -> PICbrenner8 (sprut). Go to
properties, power management and do not allow windows to turn off device to save power. Your programmer is now installed.
The next step is to calibrate the programmer. Open USBurn and go to
options -> Calibration/Test. First turn the on various voltages and
test for 5V on all but Vpp.
For SDATA ensure that the programmer reads the correct data in. Once
the main signal points check out, it's time for MCLR voltage
calibration. Turn on Vpp, and measure the zener diode voltage drop
at pin 5 with a multimeter. Enter this voltage into the
zener diode section (Z-voltage). If you used a 4.7k and 2.2k resistor
the U-divider can be left untouched, otherwise adjust it to reflect the
resistor divider' input to output voltage ratio. Once this is done turn
on both Vdd and Vpp, then hit "3: auto-adjust offset and gain". Now
push the 13V button, and finally ">" button which measures Vpp. If
calibrated correctly the voltage should be around 13V, and the voltage
measured by USBurn should be almost equal to the multimeter voltage.
Push the "graph" button to see that the boost converter is working
properly. The correct graph will look something like the one to the
right. As long as the lines pass through the green area the boost
converter section is working correctly.
I do not take responsibility for any injury, death, hurt ego, or other
forms of personal damage which may result from recreating these
experiments. Projects are merely presented as a source of inspiration,
and should only be conducted by responsible individuals, or under the
supervision of responsible individuals. It is your own life, so proceed
at your own risk! All projects are for noncommercial use only.