Here is the home page for the “MINI circuit”!


I have many years electronics experience; my MINI circuits are professionally assembled, and tested multiple times before shipping.
A home made circuit might be based on the same design but offers many chances for you to make mistakes – mistakes could damage you, the circuit or even your car!
I accept absolutely no responsility for any results if you proceed.

Build your own MINI circuit!

If you are reading this page, I assume that you already know all about printed circuit boards, Microchip PIC programming, soldering, etc, etc.
The information presented here is correct but brief – I cannot spend time “hand holding” if you have difficulties.


Here is the MINI circuit schematic in Adobe pdf format.
The design is centered around a programmed Microchip PIC16F819 (U3).
Inputs from the MINIs toggle switches are diode-isolated so that the BC1 is not affected when the MINI circuit is not powered. Outputs to the MINIs window up switches are open-collector transistors for the same reason.
The MINI circuit is powered from REG2 via D1 (reverse battery protection); an LM317HVT is used for maximum reliability and robustness. A less expensive 7805 type regulator would probably work, but is not a drop-in replacement.
Optional opto-relay U2, through diode D2, sends 12V to the ASC/DSC toggle switch to implement track mode DSC.
Optional opto-relay U1 provides a signal to trigger a garage door opener transmit; REG1 with R1 & R2 can provide a powered garage door opener output instead.
IMPORTANT: PTC1 protects the MINI circuit and the car from incorrect installation – it may be difficult to source, so you can choose to replace it with a wire link if you can ensure correct installation always!


To build a MINI circuit you first need a printed circuit board (PCB):
Top copper
Bottom copper (mirrored)

Obviously, don’t build a PCB from these .jpg files; you should use these Gerber files.
The PCB is double sided and plated-through-hole with an optional top silk screen; the size is 2.5″ by 1.75″. I use Advanced Circuits for my PCB builds
(they also have a low cost bare bones operation, but with no solder mask)


This Bill Of Materials lists all parts along with Digikey or Mouser part numbers (you should be able to find most parts easily from any electronics company, although the SMD PTC might be difficult).

Item Qty Reference Part Name Notes
1 1 PCB (2.5"x1.75") (see Gerber files in
2 2 Q1-2 2N4401 or MPSA06 Digikey 2N4401-ND
3 1 C1 1u 50V axial ceramic Mouser 80-C430C105M5U or Digikey 478-2443-1-ND
4 10 D1-10 1N4148 Digikey 1N4148DICT-ND
5 2 U1-U2 G2-1A07 Digikey CC1308-ND
6 1 U3 PIC16F819 (programmed) Digikey PIC16F819-I/P-ND
7 1 J2 18way DIP gold tipped Digikey 1/4 x S2011-36-ND
8 1 REG2 LM317HVT Digikey LM317HVT-ND
9 1 PTC1 0.14A SMD PTC Digikey MINISMDC014CT-ND
10 1 R1 1.37K 1/8W Digikey 220EBK-ND
11 2 R2 R4 220R 1/8W Digikey 220EBK-ND
12 1 R3 680R 1/8W Digikey 680EBK-ND
13 3 R5-R7 330R 1/8W Digikey 330EBK-ND
14 2 R8 R9 100K 1/8W Digikey 100KEBK-ND
15 4 R10-13 10K 1/8W Digikey 10KEBK-ND
16 1 LED 3mm Digikey P363-ND
17 1 J1 18w-18w harness (Inside Track Cabling)
1 LED designation on PCB is backwards!
2 Omit U2 unless track mode DSC is required
3 Omit U1, REG1, R1, R5 – parts only needed for garage opener versions
4 For a powered garage door opener, R1 sets the voltage (1.37K gives 9V out)
5 It seems that G2-1A07 is obsolete – I have tested both a Clare LCA110 (Digikey CLA101-ND) and an Omron G3VM-3 (Digikey Z152-ND) and both worked in position U2 to implement “track mode DSC” (I have not tested the replacements for U1 – it would be dependant on the requirements of your garage opener remote)

The 18w-18w harness has a Molex connector on the toggle switch panel end, which requires individual pins to be fitted in the correct order.
I have the MINI circuit end built with a soldered in connector but you can use a ribbon connector and soldered in plug if you prefer.
Making this cable is challenging – I made 25 then happily paid a company $10+ to make them for me!


The Microchip PIC16F819 must be programmed with correct code to implement the MINI circuit functions. A PIC programmer is required!
The source code is not available, but a machine code file can be downloaded here.


The pictures in my Gallery should be sufficient. Especially:


If you don’t understand (using the schematic) how to test the MINI circuit, the DON’T BUILD IT!
At the least I recommend that you bench test to ensure that when a 12V supply is provided (through pins 15 & 18 of J2) a 5V supply is generated to the PIC.
If the PIC is correctly programmed and the circuit is working, you should see the LED light for a few seconds then go out.
If you cannot get the LED to light then go out, DO NOT install the MINI circuit in your car. A correctly built circuit will not harm the cars electronics, but anything is possible if the circuit is built wrong!
Once you have a successful bench test, you can install the MINI circuit in your car, following the normal Installation procedure – but be extra careful to check everything.
Before I ship a circuit I verify that every toggle switch signal is successfully passed through to the car, that the dash lighting and both fog switch LEDs work, and that all circuit functions work correctly
(hold unlock to enable, hold lock to disable, auto-up windows (optional) track mode DSC, etc).
I recommend that you remove your toggle switch panel from the car and connect it to your MINI circuit – this way you can verify that holding the LOCK/UNLOCK toggle switches for more than five seconds causes the LED to flash (indicating program mode).


If you mess up, you could at a minimum blow a fuse in your MINI. It might be possible to damage the toggle switch panel or even the BC1 (a replacement will cost hundreds of dollars!);
you might even succeed in setting fire to the circuit you built, resulting in damage to the car.
Every MINI circuit I ship is first bench tested at least twice – you must take similar precautions and you must accept all responsibility.