ER-301/Teletype Connection Rev7
The first few runs of the ER-301 did not have a dedicated i2c header. Instead users would perform a small hardware modification (described here) so that they could use the exposed UART header instead.
The goal of this hardware modification is to short out the diode labeled D3 on the red CPU board on the back of the ER-301. The diode's original purpose was to provide level-shifting for the RX pin of the UART port. Shorting out this diode allows for this pin to be used for the SCL (clock) pin of i2c.
- Soldering iron (ESD-safe, reliable temperature control) and solder (recommend no-clean flux)
- Short length of solid core wire (or waste lead from a through-hole resistor or LED or similar)
- needle-nose pliers (optional)
Step 1: Cut a 7mm piece of solid core wire or use part of a lead from a resistor or LED:
Step 2: Bend it around some needle-nose pliers:
Step 3: You should have a nice boxy U-shape like this:
Step 4: Place around diode D3 like this with the bottom of the U oriented towards the bottom of the board so that we do not short resistor R62:
Step 5: And solder like this: