Friday, December 18, 2009

Servicing Heathkit IO-12 Oscilloscope

Few months back I got an old Heathkit IO-12 Oscilloscope from my friend and at the time of delivery this unit is not under the working conditions. Heathkit IO-12 is Value based laboratory oscilloscope with following technical features,

Frequency Response : 3Hz to 4MHz ≅ 5MHz
Sensitivity : 0.025V/inch
Rise time: 8µS
Sweep Range : 10Hz to 500kHz

When I remove the casing of the oscilloscope I found several damaged components (specially capacitors) and wires. After making the careful observation and testings I decided to rewire the whole oscilloscope with new components except the following,

  • 12BH7 Dual Triode
  • 12AU7 Dual Triode
  • 6AN8 Triode Pentode
  • 6AB4 Triode
  • 1V2 ½ Wave Rectifier
  • 6X4 Full Wave Rectifier
  • 6J6 Dual Triode

  • Main Transformer
  • Front end controls (including switches, potentiometers, connectors and indicator)
  • Most of the inductors
  • Cathode Ray Tube, etc

As mentioned in the above list all the Values, transformers and some of the critical components are in good condition. Only the major problem occurs at the electrolytic capacitor replacement stage(s) because in original configuration there are two capacitors packs (4 Pin capacitor package with common ground) are available. It is bit difficult to obtain those capacitors from local market. So what I'm doing is installing 4 separate electrolytic capacitors, instead of one single electrolytic capacitor pack. To do this I'm slightly change existing component layout of the original IO-12 Oscilloscope. Except these capacitor modules all other parts are commonly available in local market. (with some slight differences in packages and values)

After the rewiring, this unit work nicely and produce results as same as today's professional analog oscilloscope. At the time of testing I couple this unit with one of my old Phillips GM4585 trigger delay unit and achieve successful results. The above photograph indicate this restored IO-12 oscilloscope with 50Hz - 12.75V peak to peak sine wave.

Monday, December 7, 2009

Mini Sudoku for Windows

Sudoku is one of my favorite games and in this project we developed small computer program to play and solve Sudoku puzzles in Microsoft Windows operating systems. Like all of my other computer programs this project is also hosted in with open source – free software license (Under the terms and conditions of GNU General Public License Version 3).

This project is developed using Borland C++ and it had following general features,

  • Sudoku Game Panel with multiple user profiles
  • Support custom board styles
  • Auto-play options for all the predefine and user specified puzzles
  • Minimize to tray option
  • Three game play levels (as easy, intermediate and hard)
  • Easy to add any number of custom puzzles

Latest version of Mini Sudoku is available to download at and at Mini Sudoku Ohloh project page.

To modify this project user need to use Borland C++Builder 6, NSIS (Nullsoft Scriptable Installer) and Adobe Photoshop (or any other image editor which is capable to modify Photoshop psd files).

Friday, December 4, 2009

12V DC to 230V AC Inverter

In this project we design an Inverter to convert 12V DC power source to 230V AC power. This system consist 3 main stages such as oscillator, switching circuit and step up transformer stage. In oscillator we use 4047 CMOS astable multivibrator to generate nearly 60Hz oscillation.

In a given configuration,

f = 1/(4.4C2(R1+R2))

f = 1/(4.4×(0.1/106)((3.3+33)×103)))

f = 62.609 Hz

In a switching stage we use 2SD400 NPN transistors and IRFZ44 N-channel FETs. For the step-up transformer it is recommended to use 12V-0-12V : 230V – 5A transformer.

When constructing the circuit it is highly advisable to apply good heat sinks to both Q1 and Q2. If you are plan to use single heat sink to both Q1 and Q2 it is required to place good insulator between the transistors and the heat sink.

During the field test we use 12V - 7Ah sealed lead acid battery (which was commonly used in general UPS) with this system and constructed prototype deliver 238V AC in no-load.

To get the complete circuit diagram and Eagle PCB design please check the google drive.