MHz Display Blaster

A clone of the TD-37S 2-digit MHz display that was common in 386/486 PC cases. It can display a Turbo and a non-Turbo number, depending on the state of the Turbo switch. It also drives the Turbo LED accordingly.

Assembly Tips

• Video showing the assembly of rev.0.1 PCB: https://www.youtube.com/watch?v=a4iVehn7APU

Warning Please solder the single-row header and the resistor before you solder the 7-segment display

Connecting the board to the PC

• Power: The display is powered by providing 5V to the + pin of J4 and GND to the - pin.
• Turbo Switch: The turbo switch is a 3-pin 2-way switch. Connect the common wire (middle) to CM, the Turbo-ON wire to T and the Turbo-OFF wire to N (J4).
• Turbo LED: The turbo LED is connected to L and P on J4. P is the positive.

Display Configuration

• Each segment of the 7-segment display is configured individually with a jumper
• Each segment corresponds to a pin in the configuration headers
• You can short that pin with one of the neighboring state pins (forming a T shape) to set its state, which can be one of the following:
  1. ON when Turbo switch is OFF (jumper to position 1)
  2. ON when Turbo switch is ON (jumper to position 2)
  3. Always ON (jumper to position 3)
  4. Always OFF (no jumper)

Note Please note that the PCB is often mounted up side down on the case.

• For a simple tutorial on how to set it up please refer to the video: https://www.youtube.com/watch?v=wNkg-e47Ex8
• More resources on MHz Displays

Bill of materials

Gerber files are published in the releases: https://github.com/scrapcomputing/MHzDisplayBlaster/releases

Reference	Quantity	Value	Footprint/Comments
U1	1	(e.g., LTD-6440G)	18-DIP (0.600", 15.24mm distance between top and bottom row pins) 2-Digit 7-Segment Display Common Cathode 0.56" Green
J1 J2	2	Conn_02x15	Connector Male PinHeader 2x15 P2.54mm Vertical
J4	1	Conn_01x06	Connector Male PinHeader 1x06 P2.54mm Vertical
R1	1	>= 39 Ohm (100 Ohms recommended)	1/4 Watt resistor. The original TD37S has a 39 Ohm resistor. But the resistor value is specific to the type of the LEDs used. The original ones operate at around 2V, so the resistor drops 3V. Higher resistor values make the display more dim, but are also better for the longevity of the LEDs in the display.
Jumpers	15		2.54mm pitch jumpers

Changelist

• Rev.0.2 : Fixes polarity issue, improves info
• Rev.0.1 : Initial revision