SADARC membership card 2025 PCB

[Josh]

Hi, So i've committed some time to making a standalone SDR to go on the back of the clubs member ship card. Here I will detail the progress and details.
I want to replace most of the original through hole components with SMD and also make it very clear as to the what everything was and layout it just a bit tighter. So far I've added the new SMD parts, two more push buttons, and redone the LPF and switch. I've also adding some test points that i think are missing. Also attached is the partial BOM ~$19ea.

 

[Josh]

Added LNA.

 

[Josh]

added Tayloe Quadrature Product Detector. Still got a little room to play with. maybe an audio amp, battery charger, or si5351(although a bit small to solder at home for most people). I might just go for a connector for a SPI display?

 

[BillC]

Hi Josh, which type of VFO will you use with the Tayloe detector? Freq x 4 takes 28 Meg up to 112 Meg for the VFO frequency. Will programming then provide the correct screen frequency read out, allowing for the times four offset as it were? Looks like an interesting project. I would like to tag along too. Good luck.

 

[Josh]

The VFO is the on the PIO module of the rp2040 its is clocked at the sysclk, which can be adjusted between 125 - 133 Mhz.The best sys clock and PIO PLL divider is picked for any arbitrary frequency. Its not perfect but its good enough.

The PIO is a small programmable digital IO state machine. It generates the quadrature , here is its assembly code.
```
.program nco
set pins, 0
set pins, 1 ; Drive pin low
set pins, 3 ; Drive pin high
set pins, 2 ; Drive pin low
```

 

[Josh]

sorry I missed the part about the correct read out of the frequency, yes, the function that sets the sysclk and pll divider for the PIO returns the calculated best fit frequency used, the VFO NCO (numerically controlled) output from the pio works out to be ~ +/-8kHz of the desired frequency. The ADC has a bandwidth of 250KHz and the software does the rest of the fine tuning.

 

[BillC]

Hi Josh, thanks for the explanations.It is truly amazing that all the functions can be made to work in those tiny IC's. Watching with interest.

 

[Josh]

updated BOM with all the passives. added twice the number of passives as they tend to get lost.

 

[Josh]

PCB is just about ready to order, Probably later today. Order has been placed with digikey for some parts.

 

[Josh]

 

[Josh]

The box of parts for the Badge proto type turned up.
I need to check the footprints for everything, and things like the switch contacts on the headphone jack etc.

There is enough parts for 5 off.

 

[Josh]

denys and I trying out a build.

works. not sure how well yet, had to break for food.