As I become more familiar with KiCAD, I wondered what else I could draw up. This coincided with Stuart Mackay having some problems with a bad batch of DM More Pro Mini and I wondered if I could do a DM More copy, but more customised to our use. After discussing with Stuart his wish list, we came up with the following:
- Same 40mmx40mm dimensions of a Pro Mini Strong
- Pin compatible with the Pro Mini Strong, so it would run Phil's 7 channel encoder or my modified "F3A" version of his encoder without program change
- The battery in and encoder power out connectors in similar positions to existing, with no "links" needed
- Reverse polarity protection (we remove the DM More Pro Mini Strong reverse polarity protection Schottky diode, to fit the link to get the battery voltage to the 3-pin ppm/power for the 2.4GHz module)
- The sounder to be on-board and to be powered directly off the battery voltage, so it doesn't put an additional load on the voltage regulator. Still use an emitter-follower so it stays as a 5V sounder
- A zener diode and pot' to drive the existing meter on most transmitters - the pot to adjust full-scale deflection
- The DIP switch pads the correct distance apart (0.3"), so the legs don't need bending/forming to fit
- Fit another row of pads 0.1" apart, so two rows of headers could be fitted for use with standard "jumpers", as an alternative to the DIP switch
- Split the analogue inputs into two banks of four with a small gap between them, as it's difficult to fit 8 plugs into the existing header - most servo plugs are fractionally wider than 0.1", so the last plug to be connected are always displaced sideways and difficult to connect
- Omit the reset switch and the D13 header, as the sounder is onboard and connected via a transistor to D13
- A red smd LED for power and a green smd LED on D13 to indicate the sounder
- DIP switch Sw2 not connected to D0, so if it is accidentally switched, it won't short the ppm signal to ground (it saves cutting the legs of Sw2
But before I had even received the boards, I'd already designed a MK2 version with some other idea's. The sounder was very close to the DIP switch and if a different brand of DP switch was used it could foul the sounder. And it seemed a shame to have to solder a through-hole zener diode on-board and not have a surface mount version. I always use a 6.8V zener for the meter and Phil uses a 6.2V zener, hence why I thought you'd fit one to suit. But I realised I could put a 6.8V and a 6.2V smd zener on the board, on different pins of a 3 pin header and the cost would be less than one through-hole version.
I then did an MK3 version to use the ATmega328PB, the follow-on-model to the normal ATmega328P used in Arduino. It has two additional inputs (it changes a 5V and a GND connection for the additional inputs). We could use one to wire up all 8 of the dip switches as there wouldn't be a conflict with the ppm signal on D0. And I've added a low voltage alarm circuit using a zener and transistor. Not everybody thinks that a low voltage alarm is essential, but if it would fit, why not? And the other switch? Well I know some are already using the modified "F3A" version of the encoder, others like Phil, still prefer the original. There's plenty of flash memory to have both programs integrated together and Sw2 Off = original and Sw2 On = F3A.
I've sent out a number of the boards to members on the forum for comment and also ordered some MK2 and MK3 boards, to compare.
Cheers
Mike