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Sunday, 16 February 2014

My Minima Progresses


Following a whistle-stop tour of the Middle East, I am back and have done some more with my Minima. After much deliberation and head scratching, I have decided to box the linear amplifier and Low Pass Filters separately. This way I can re-use the amp later for other projects should I decide to do so.

So here's the finished Minima:

You will see that I have used a DIN socket to take the BCD band selection information from the processor to the rear panel, this will allow me to automatically switch the LPFs in the linear as the radio tunes. I have also added a simple PTT line to the rear panel to switch the linear into TX.

Here's the linear and filters in a state of incompleteness:

So, the BCD output is configured in accordance with this table:

I've included 6 low pass filters with the frequencies listed in the column TX LPF above. So as the radio tunes when the frequency passes one of the thresholds the output binary value is set on the three lines I have attached to the DIN socket. The only thing to note is that the 19MHZ TX filters is engaged with BOTH the 15MHz and 30MHz TX filter. This has meant I have to use a simple diode matrix on the output of the 4028 CMOS chip to enable the same filter on two different outputs. So in the linear box we have the 4028 CMOS BCD converter plus a DIL package with darlington pairs to physically switch the relays.

If you need a schematic of the linear control wiring that takes the BCD signals from the processor and switches the LPFs email me and I will create one.

I've made a few modifications to the software, including the logic needed for my LPF switching in the linear. Rather than explain all the details I have simply uploaded my code here:

If you were to use the most excellent utility Beyond Compare to create a difference listing between my version and the original, you would be able to see the changes very clearly.

So, on with the linear....

Good, egh?


  1. Waw! Quite impressive. But is the Minima really DIY stuff or PhD dissertation on Arduino Coding?

  2. well said PaulC,
    What Mark did is no less a PhD work on minima. best of times to him.

  3. I hoped that the code changes were quite easy to understand and well commented? I think PhD is somewhat wide of the mark. I have used Arduino for quite a few projects in the past so perhaps had a head start. But we can all learn from our projects.

  4. Great work Mark. Coming together very nicely!