Hydra Card with Protoboard

blittled

I've been thinking of wiring an expansion port onto the protoboard that will interface with Hydra cards and I have two questions:

1. The 3.3V and 5V loopbacks look like they are just tied to the power rails so what function do they serve?
2. If I get the 128K eeprom expansion card will it conflict with the on board 64k eeprom or does it just mean the on board 64k will be a copy of the lower 64k of the 128k?

▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔
What electronics need - MORE POWER!!!!!!!

Mike Green

The 3.3V and 5V loopbacks provide an indication that the expansion card is in place ... a source of +3.3V and +5V. On the Hydra, this is used to disable the on-board 128K EEPROM by moving it up in the I2C address space to the 2nd 128K space.

If you connect the expansion card socket to the pin 28/29 I2C bus, then the expansion card 128K EEPROM will conflict with the on-board 64K EEPROM. Best thing would be to use some other pair of pins for the expansion card I2C bus. The several I2C drivers can access EEPROM on other pairs of I/O pins, not just pins 28/29.

If you want to use the expansion card EEPROM, you'll need to modify the EEPROM on the Protoboard just like on the Hydra so the A0 address line (I think that's the one) is connected to the loopback with a pulldown resistor to ground for when the expansion card isn't present.

blittled

Thanks Mike! That clears things up for me. I may just add another 128K eeprom on my protoboard and use a dip switch to ground with pullup resistors on A0, A1, and A2 so I can have configurable addresses on pins 28/29.

▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔
What electronics need - MORE POWER!!!!!!!