Despite my experiments with the MCP23017 last week, I'm using the Mircochip MCP23008 I/O expander to control four filters, one of which is switched into circuit by relays. The switching is controlled by I2C messages from my RF Generator, which is in essence an Arduino.
I have used a common board layout for switching part of the system and inserted band-pass and "harmonic" filter networks, both of which are to standard G-QRP Club recipes...
There are jumpers to set the I2C address of each board - but in use they will share the same address, such that both MCP23008s respond simultaneously to the band-change request. The I2C input (which also supplies 5V power) is at the left of each board, whilst the relays are switched by 12V, supplied by an input on the opposite side. RF enters the boards stage right and leaves on the left.
The boards are only single-sided PCBs, made in my "back-yard PCB fab", so I had to add some additional wiring on the copper side to control the output relays...
In use, the boards will be stacked, in an attempt to save space - it worked for the Tokyo city planners. Here's the intended configuration...
I have built filters for 80,40,20 and 17m - the first three are my favourites on the new rig and the 17m band is an experiment.
The system works FB - but I haven't yet had chance to plumb it into the rig - I've run out of weekend, not helped by spending a couple of pleasant hours at the West Manchester Club's "Red Rose" Winter Rally earlier today, where I didn't do any significant damage to the bank account.
...-.- de m0xpd
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