Pi1541io Revision 2

On Friday, I received the prototype batch of PCBs for the second revision of my IO Adapter for the Pi1541 project. Today, I finally found the time to assemble a couple of those boards and so far, everything seems to be working great!

Two working configuration of the Pi1541 IO Adapter.

When assembling one of the rev.2 boards, there are multiple alternative configuration to chose from. One of the simplest working ones — shown on the left side in the photo above — needs only three components: a 6 pin DIN connector, a 4 channel level shifter module, and a 40 pin female header to connect to the Raspberry Pi. Most of the possible configurations can be built using easy to solder through-hole components, only!

The Level Shifter

All configurations require voltage level converters. The PCB layout allows you to either use a cheap and ready-made 4 channel module or to fit the same SMD components that the module contains directly to the board.

Voltage level converter options: SMD components directly on the PCB (left), or a ready-made module (right).

Technically it doesn’t make a difference which one you chose. Using the module will relieve you of the need to solder SMD components in case you are hesitant to handle those.

The Bus Driver

On his project page for the Pi1541, Steve White currently describes two different options for wiring the Pi1541. “Option A” simply uses a 4 channel level shifter to connect the Raspberry Pi to the Commodore serial bus. This works fine, but you risk damaging the RasPi when connecting three or more devices to the bus. “Option B” requires an additional 7406 logic IC to drive the bus. The Pi1541io board must be configured for one of these two options using solder bridges on the bottom side.

Configure the bus driver using solder bridges.

Note that you also need to tell the Pi1541 software which bus driver you are using by changing the options.txt file. Please see Steve’s instructions on how to do this. If you configure your board for “option B” the following components are required:

  • 7406 logic IC (U2)
  • 100nf bypass cap (C1)
  • two 1kΩ pull up resistors (R3, R4)

With “option A” these components are not required.

The SRQ Signal

Also on the bottom side of the PCB there is a place for components to add an optional 5th level converter channel that connects the SRQ signal from the serial bus to the Raspberry Pi. This signal is not used by the C64 and currently it isn’t used by the Pi1541 either. So, there is no need to fit those components now.



Other Components

Most of the other components are optional too, actually. Some of them are very useful though, like the 5 push buttons. Others are probably better left our for now, like the piezo speaker. I would recommend to fit at least the two LEDs with their resistors and the five push buttons SW1-5.

This is the current BOM updated from the first revision:

1 P1 2×20 pin female header eBay
1-2 IEC1-2 6 pin DIN socket eBay
5 SW1-5 right-angle push buttons eBay
1 U1 4 channel level shifter module eBay (China) eBay (Germany)
1 U2 7406 IC eBay (China) eBay (Germany)
1 C1 100nf ceramic capacitor eBay (China) eBay (Germany)
1 SW6 push button (optional) eBay
1 D1 3mm green LED  
1 D2 3mm red LED  
2 R1,R2 resistor 220Ω  
2 R3,R4 resistor 1kΩ  
5 Q1-5 BSS138 FET SOT-23 eBay
10 R5-12, R14, R15 resistor 10kΩ, 0805 SMD  
1 R13 resistor 1kΩ, 0805 SMD  
1   piezo speaker (optional)  
4   M2.5 screws, 18mm  
4   M2.5 nuts  
4   distance rolls, 11mm  

In addition, you’ll still need a Raspberry Pi 3B or 3B+, a micro SD card, a good power supply, and a Commodore serial cable.

What next?

I will distribute the remainder of my prototype batch of PCBs to people on Forum64 for further testing like I did the last time. I would actually recommend to wait for those results to come in. If you absolutely cannot wait any longer to try this yourself, here are the Gerber files for you to download. As always: use at your own risk. I’m not responsible for any damage you might cause to your hardware, to yourself, or to anyone else.


10 thoughts on “Pi1541io Revision 2

  1. Thanks for your feedback! But no, I’m currently not considering selling assembled boards.

  2. looks amazing and really clean. Is the plan to sell the boards and if so, do you have a idea for when they might be available?

  3. Just wanted to say thanks! This is a great looking board. I have ordered all the parts I need to build 5 of these. Glad to see you get 10% commision on these by the way. Now just have this eternal wait for everything to arrive… Will let you know how it works out after all this stuff arrives and I get one up and running.

  4. Hi,

    Thanks for this PCB 🙂 My PCB’s just arrived from PCBWay.
    I was just going to try Option A but I have a few questions.
    Rather than use a DIN socket and then a lead, I was just going to wire in a short length of cable with a DIN plug. Can I wire straight into IEC3? I was going to open out the DIN PCB connector holes at the bottom of IEC2 (earth holes not signal!) and use a cable tie to secure my short DIN cable.
    Could you tell me the PIN OUT for IEC3 Left-to-Right please.


  5. Hi Sean,
    You’re welcome! That is exactly what the IEC3 connector is indented for. Except maybe for the cable tie thing but that should be ok, too. 🙂 The pin numbering is the same as on the Commodore IEC connectors and pin 1 is marked on the silk screen.

  6. The first prototype batch for rev.3 has been produced in China and is on its way to Germany. 🙂 Once I have those boards, I’ll assemble one and post the results.

Leave a Reply

Your email address will not be published. Required fields are marked *

This site uses Akismet to reduce spam. Learn how your comment data is processed.