Notes:
- Make sure the MCP1702 is used and not the MCP1700. The MCP1700 can only handle up to 6V.
- The ATTINY85 should be mounted in a socket to make it easier to update or reprogram. The 4n37 optocoupler can be soldered to the PCB.
- Use a 4n37 and not a 4n28 or other optocoupler.
- If the large M7 diode isn’t labelled on your PCB, it’s the largest unlabelled diode (labelled M7 below).
BOM:
Qty | Value | Device | Package | Parts | Description | Source 1 | Source 2 |
|---|---|---|---|---|---|---|---|
| 1 | LED | LED3MM | LED1 | LED | |||
| 1 | 100k | Resistor | R0805 | R21 | RESISTOR | ||
| 1 | 100n | Capacitor | C0805K | C5 | CAPACITOR | ||
| 2 | 1k | Resistor | R0805 | R3, R4 | RESISTOR | ||
| 1 | 1n4148 | Diode | SOD323-W | D8 | DIODE | ||
| 2 | 1u | Capacitor | C0805K | C1, C2 | CAPACITOR | ||
| 1 | 220r | Resistor | R0805 | R15 | RESISTOR | ||
| 1 | 2k | Resistor | R0805 | R1 | RESISTOR | ||
| 1 | 3.9k | Resistor | R0805 | R20 | RESISTOR | ||
| 1 | 4N37 | Optocoupler | DIL06 | OPTOCOUPLER | 6-Pin Phototransistor Optocoupler | ||
| 2 | BAT54S | Diode | SOT23 | D3, D4 | Schottky Diodes | ||
| 1 | M7 | Diode | DO214AC | D1 | DIODE | ||
| 1 | MCP1702-5 | LDO Power Regulator | TO92 | IC1 | 5V LDO VOLTAGE REGULATOR | ||
| 1 | MIDI Connector | Panel | MIDI-IN | Female CONNECTOR, DIN 5-180, Panel Mount. | |||
| 2 | 3.5mm Jack | THONKICONN | CLOCK, START/STOP | 3.5mm socket for Eurorack modular synths | http://shop.erthenvar.com/collections/accessories/products/3-5mm-inline-jacks | https://www.thonk.co.uk/shop/3-5mm-jacks/ | |
| 1 | Tile power lead | "Futaba J" style Tile power lead | http://pulplogic.com/product/tile-tail/ | ||||
| 1 | ATTINY85-20 | DIP08 | U1 | Atmel 8-pin 2/4/8kB flash uC | |||
| 1 | IC Socket | DIP08 |
Schematic:
Build Instructions:
Clean PCB with isopropyl alcohol to remove any manufacturing residues.
If necessary, separate panels carefully by gently flexing and twisting back and forth, ensuring that they break cleanly at the “mouse bites”. File the leftover tabs down until flush with the edge of the panel or PCB.
Solder the surface mount devices.
Solder the through-hole parts, including power lead, but NOT the jacks, LED, or MIDI connector.
Prepare the MIDI connector by trimming lugs 1,2,3 (two outer lugs, and middle lug.) Cut them as close to the bottom as possible so they won’t scrape the PCB. Bend the two remaining lugs and ground lug vertical.
Mount the MIDI connector to the front panel using two m3 screws and bolts. Test-fit the panel to the PCB, bending the MIDI lugs to line-up with the PCB holes.
Solder the two jacks and the LED, using the front panel for alignment. DO NOT SOLDER THE MIDI CONNECTOR YET. Use the two 3.5mm jack nuts to hold the panel and MIDI connector to the PCB.
Check that there is no contact between the MIDI Connector and other components, particularly the power regulator leads and the optocoupler pins. Trim down any leads that looks like they could cause a problem.
At this point the MIDI connector should be making good contact with the PCB without soldering to allow for testing.
Check soldered connections for shorts, especially between the pins of the BAT-25S diode.
Apply power and check that pin 8 is getting 5V. If not check again for shorts.
Add the programmed microcontroller, and again apply power. The LED should flash briefly. Connect a MIDI cable (attached to a sequencer) and start a sequence. The LED should flash and CLOCK output should be sending a stream of pulses. If the sequencer is sending Start/Stop/Continue messages then the START/STOP output should go high when the sequencer starts, and go low when it stops.
If everything is working as it should, then tighten the nuts and solder the MIDI connector on the back of the PCB. Once it’s soldered the front panel cannot be removed without desoldering the MIDI connector.
Done!