Shared projects

Z80 Test Circuit

by SyncChannelBlog.

2 layer board of 2.25x2.75 inches (57.15x69.85 mm).
Shared on September 23rd, 2017 20:36.

This board implements a classic Z80 microprocessor test circuit. All data pins are pulled low, causing it to execute the NOP instruction $00 repeatedly. The program counter increments and the activity on the address lines is visualized using LEDs. A slow clock signal is applied to make the address bus activity slow enough to see.

The MREQ and RD pins are also brought out to LEDs. Push buttons are available for the RESET and WAIT lines. The clock signal is generated using a 555 timer.

The board is powered by applying 5V to the 0.1" header pins. Reverse polarity protection is provided using a P-Channel MOSFET.

This board is mostly a novelty. It’s really cool to see the program counter increment on the address pin LEDs and the MREQ and RD LEDs flash. It is not possible to execute an actual program on this board, as it has exactly one byte of “memory” with the contents $00. :)

BOM

  • U1: Zilog Z80 40DIP
  • U2: 555 Timer 8SOIC
  • Q1: Alpha & Omega AO3401A P-Channel MOSFET SOT-23 or similar
  • R1-R19, R21-R22: 1k 0603
  • R20: 22k 0603
  • C1: 10 uF 0805
  • C2, C5: 1 uF 0603
  • C3-C4, C6-C7: 100 nF 0603
  • RN1: 1k, 8 resistor (9 pin) SIP
  • A0-A15, MREQ, RD: 0805 SMD LEDs (colors of your choice)
  • RESET and WAIT switches: SPST tactile switch Through hole
  • 5V header: 1x2 0.1" standard header pins

Notes

  • R20, R21, and C5 set the 555 clock signal frequency. The values provided above will set a clock of approximately 32 Hz. You can use an online 555 calculator to pick different values and adjust the clock frequency as you like. In relation to the classic 555 circuit schematic: R21 on this board = R1, R20 = R2, and C5 = C.
  • Brand new Z80 microprocessors are available on Digikey if you don’t have one.

Eagle Files

https://github.com/SyncChannel/Z80-Test-Circuit

Other References

http://www.z80.info/z80test0.htm

https://z80project.wordpress.com/2014/02/09/z80-test-circuit/

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20 Input AND Gate

by SyncChannelBlog.

2 layer board of 2.50x2.20 inches (63.50x55.88 mm).
Shared on September 16th, 2017 19:31.

What to do when you have a partial reel of 74AHCT08 chips burning a hole in your pocket? Design a 20 Input AND gate of course.

Yes, this actually works. There are 10k pulldowns on all inputs so that they won’t pick up on noise. Apply logic high signals to all inputs to test it.

I made this board just for fun. Perhaps it would make for a good SMD soldering challenge… I gave one to a Digital Electronics professor who was retiring and he loved it.

BOM

  • U1-U5: 74AHCT08 SOIC-14 (or similar logic family)
  • U6: 74LVC2G17 SOT-23-6
  • D1: B340A Schottky Diode SMA
  • PWR LED: 0805 SMD (color of your choice)
  • HIGH and LOW LEDs: 1206 SMD (colors of your choice)
  • R1-R3: 330 ohm 0603
  • Pulldown resistors (back side): 20x 10k ohm 0603
  • C1-C6: 100 nF 0603
  • C7: 10 uF 1206 SMD 10V (or substitute with ceramic cap)
  • 2 Pin Headers: 1x2 0.1" standard header pins
  • 40 pin Header: 2x20 0.1" standard header pins

Eagle Files

https://github.com/SyncChannel/20-Input-AND-Gate

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VGA Blinken w/ Connector

by SyncChannelBlog.

2 layer board of 1.50x1.25 inches (38.13x31.78 mm).
Shared on December 31st, 2016 02:18.

Modified version of the “VGA Blinking Lights” PBC by Danjovic:

https://github.com/Danjovic/VGA_Blinken

https://hackaday.io/project/8537-vga-blinking-lights

This version of the PCB has SMD passives to save space, but adds an onboard DB-15 connector for easy connection to a monitor. The PIC microcontroller is still DIP and socketed to allow for external programming.

See the original project page for the parts values, firmware, etc. The passives on this version are 0603. The DB-15 footprint is for a standard through-hole, right angle connector (Amphenol FCI ICD15S13E6GV00LF or similar).

It’s no longer 1" square, but it’s a lot easier to hook up that monitor with the onboard connector!

Eagle files shared on Github:

https://github.com/SyncChannel/VGA_Blinken_Modified

Original version of the PCB on OSH Park:

https://oshpark.com/shared_projects/BGKXsEzu

All credit goes to Danjovic, the original creator. This is an awesome project.

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such Laen!

by SyncChannelBlog.

2 layer board of 1.00x1.00 inches (25.43x25.43 mm).
Shared on July 25th, 2016 23:15.

Through-hole resistor breakout board. The large resistor footprint accepts up to a 1 Watt resistor. The 2-pin header accepts standard 0.1" breakaway header pins.

Much OSH Park, don’t you think?

Very inspiration: https://oshpark.com/shared_projects/YyIz7BEX

Many blogs: http://syncchannel.blogspot.com

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Retrokit SAM D Edition 2016

by SyncChannelBlog.

2 layer board of 1.00x1.85 inches (25.43x46.99 mm).
Shared on July 14th, 2016 02:05.

http://syncchannel.blogspot.com/2016/07/atmel-retrokit-sam-d-edition.html

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