Default options on their service are OK for this board. If you are new to this, mine were built with Seeedstudio’s $4 PCB service.
Alternatively the code on Arnie’s repository will work – provided that internal pull-ups are enabled on PB1 and PB2. I have made quite a few alterations from the original implementation – adding “Redial” functionality, as well as simplifying the programming of speed dials.Īs previously mentioned, in my implementation the AVR is in power-down mode during all idle times, essential when building my version of the hardware. We don’t need that transistor either – this has been replaced by a resistor (R1) which effectively does the same thing, with the AC path now through the VCC pin of the AVR, then through the 78L05.įitted to a 332F (Wedged under the 303A key) My version of the code I also removed the resistors on the HW de-bounce circuit, now utilising the AVR’s internal pull-ups. This also happens to fix the BT landline problem, as that was simply that the tones were too quiet, thanks to it attenuating its own output! Having a 78L05 fixes all of this, and we can do away with that 200uF capacitor while we’re at it. We can see how this problem sneaked in: R1 of the original design was first specified to be 2K, which kept impedance in check, but left it with a voltage droop problem, this was revised to 220 ohm, which fixed the droop problem, but then meant the adapter was shunting the line through the 200uF capacitor.
By replacing the Zener and Resistor arrangement with a 78L05 – the AC load is virtually nothing, meaning speech volume is now the same as it was before installing it. The main change to the design is the power supply.
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