Wednesday, March 27, 2013

Refurbish C64 Power Supply Unit

This is a quick post regarding my Commodore64 Power Supply restoration. This C64 is my first computer and two days back its power supply get burn because of some short circuit in its output connector. This is a first time I open this C64 PSU and its internal circuitry is really simple to track down.

Commodore64 Power Supply Unit

Main component of this PSU is its 6 terminal step-down transformer. Other than that its circuit it limited to 2 rectifier diodes, 7805 positive voltage regulator, 2 - 1W resistors and 4700µF/16V electrolytic capacitor.
In my C64 PSU, defective component is 7805 voltage regulator, once I replace it and rewire the output terminal its starts to work again (like good old days).

Commodore64 Power Supply Schematic

Above diagram illustrate the schematic of my C64 PSU (which I was traced using original PCB). The high resolution images of PSU, are available at my flickr photo collection.

Saturday, March 23, 2013

DIY Liquid Level Monitor and Automatic Control System

This is an easy to build "liquid level monitor" and "automatic control system". This control system is mainly based on Microchip’s PIC16F630 8bit MCU and few combinatorial logic ICs. This system is specifically design for industries where there is a requirement of maintaining a liquid level at a particular level. The level monitoring stage of this system can capable to sense up-to 8 liquid levels and its trigger point can be programmed at anytime by using its simple 2 button user-interface.

This system is design to work with 12V (or maximum of 25V) DC power source and its sensor system is capable of sensing liquids with resistance of up-to 30k to 35k. To minimize the sensor noise and output instability, the control software is equipped with simple 20-tap FIR like filter system.

The output stage of this system is design to work with 12V to 24V DC relays and it is recommended to use Tyco K10 series or similar kind of relay with this system.

The trigger point of this system is easy to define and it can be done by using S1 and S2 tactile switches. Once user press the S1 (MODE) switch the system enters into programming mode (and that stage trigger point LED starts to get blink), after that user can select desired trigger point by pressing the S2 (SELECT) switch continuously. Once new trigger point is set user can leave the programming mode by press S1 switch again.

The control software of this system is developed using Microchip’s Hi-Tech C compiler and it is available to download with GNU GPL license. This system consist with some sensitive CMOS ICs, so make sure to take necessary precautions while assembling and installing of this system (specially take care about the sensor probes).

As a sensor probes use any suitable low resistive conductor (e.g: copper or aluminum wire) and make sure that it is not reactive with the target liquid type.

This DIY "Liquid Level Monitor and Automatic Control System" is an open hardware project. All its design documents and firmware source codes are available to download at All the design documents of this system are released under the terms Creative Commons Attribution 3.0 Unported License and firmware source code is release under the terms of GNU General Public License 3.0.