Saturday, May 28, 2016

Modified Heathkit HD-1410 electronic keyer

HD-1410 is quiet popular iambic keyer which is manufactured around 1970's by Heathkit. The original HD-1410 keyer is designed using 5 commonly available 74LS series TTL ICs and 8 transistors. Other than iambic operation it has an option to adjust sidetone frequency and support for (external) single-paddle key unit.

In this project we redesign original HD-1410 electronic keyer with today's commonly available components. In this new design the key components which we replace are transistors, diodes and power supply section of original HD-1410 circuit. Most of the NPN transistors in original design are replaced with KSP42 and KSP10 transistors, and all the PNP transistors are replaced with KSP92 transistors. To keep everything simple we also use same TTL chip-set with this new design.

PCB of modified Heathkit HD-1410 electronic keyer.

Tested PCB layout for this new keyer is available in the project archive and this PCB layout is based on standard though hole type components. Dimensions of this PCB is 110mm × 102mm.

We test this modified HD-1410 design with several transceivers and it performs extremely well. This new design also behaves similar to original HD-1410 unit and the parameters which got change are DC input voltage range and power consumption only.

Schematic, PCB and wiring diagram of this modified HD-1410 keyer are available to download at elect.wikispaces.com. The original Heathkit HD-1410 schematic and details are available at http://www.heathkit.nu/heathkit_nu_HD-1410.html.

Sunday, May 1, 2016

Simple crystal tester

This is simple Colpitts oscillator to test commonly available passive crystals which range between 2MHz to 27MHz. This unit must connect to an oscilloscope and/or frequency counter to get the frequency of the crystal.

This circuit is design to work around 9V to 12V DC power source. Both 2SC930 transistors can replace with any high speed NPN transistor such as 2SC829, 2SC933, etc.

Testing 5030kHz FT-243 crystal using prototype version of crystal tester.

In our lab we use Manhattan style layout to prototype this crystal tester and it produces highly accurate results with above specified frequency range. According to our observations, after 27MHz, amplitude of the waveform starts to decrease steeply.

Schematic and Stripboard wiring layout for this crystal tester is available to download in here.