The old Sun Tachometer has been on a shelf for over 40 years and I figured it was time to get it working. The problem was the Mercury batteries had failed long ago and corroded the inside of the transmitter box. The transmitter is the Achilles heel of these old tachs. The transmitter circuit consists of batteries, capacitors, and a relay, all of which are prone to failure over time. The meter movement is very well made and if you have ever held one in you hand you can tell it's a quality piece. This tach will look great on the steering column of my '56 Chevy. My plan was to put together a solid state circuit to replace the electrical/mechanical guts of the old transmitter box. I used a monostable multivibrator circuit using two common NPN Bipolar Transistors to generate an adjustable square wave signal to drive the meter movement. The timing of the output is controlled by an RC network. This video is a test of the circuit with the components mounted on a breadboard. The test was a success so I ordered a printed circuit board that will mount inside the original transmitter box. I used EasyEDA software to lay out the printed circuit board. EasyEDA is free and after playing around with it I found it easy to use. When finished I generated a Gerber file that any PCB manufacturer can use to build a circuit board. JLCPCB in China is building 5 circuit boards for $2 plus $9.80 shipping. $11.80 for 5 circuit boards is a good deal. The rest of the parts consist of 8 resistors, 4 capacitors, 2 diodes, 2 transistors, and 1 trim pot. these are common parts and dirt cheap. The PCB's should arrive from China in two weeks. I will let you know. I used timing light to calibrate the tach by adjusting the trim pot. Hope you enjoy the video.