A few explanations about the current layout:
This is a prototype, so to save cost the Hadron & Quantum heaters are both in the same board, on opposite sides, to save cost on proto boards.
The production boards will probably be separate boards/designs, assuming i get more than a couple requests for Quantum sizes.
Though the picture shows all parts mounted, only those relevant to the version requested will be installed;
- the threaded bosses and connectors in particular would get in the way otherwise
Note the threaded bosses selected are M3 thread, 3mm high, but 4 or 6mm are available too, if that's more convenient to leave room for insulation,
however its probably best to add extra insulating washers if you want it higher off the carriage plate.
There is a surface-mount thermistor connected to the center standoff mount ring; the center standoff wont be installed unless you specifically request one- it should not be connected electrically to the carriage plate if the built-in thermistor is used. There is an additional thermistor about 1/4 of the way in from the edge if you prefer that and then you can cut the tracks to the center one to use that as a mounting point instead. The center standoff is there mainly to support the Hadron side, it cannot be mounted on the opposite side at the moment.
For the Hadron there are 4 red LED's along the front edge under the board; this will reflect off the carriage plate and i expect it to produce a nice visual effect.
For the Quantum the LED's are in the 4 corners on top;
the board is made a little longer in this case to allow a square piece of glass to fit between the LED's, which could
serve double duty to help keep the glass in place.
The LED's are powered from VIN and switched to ground using a separate signal; i may add a transistor switch & constant current regulator in the final layout to make it easy to interface to any MCU. i prefer this option so you can have the MCU flash the LED's the entire time while the plate is reading above a certain temperature threshold, rather than only while the heater is energised. If you prefer the latter you need only connect the LED signal to the heater switch input.
The extension on the back of the Quantum heater on one side allows the connectors and config solder shunts to be accessible on the top side, which is necessary to allow both boards to be combined into one. If i get at least a dozen orders for Quantum, i will adjust the layout to place the connectors etc on the back side like the Hadron.
The different voltages are configured by adding or removing solder blobs on special shorting "shunt" pads; they will come pre-blobbed for 12V unless you specifically request otherwise. The production units will have an easy to read chart printed on the underside showing which locations to make short or open for each voltage.
The flex cable "experimental" option uses standard 1mm pitch x 30 FFC cable. In theory it should not act as a heater as well
but i will test that thoroughly before recommending others to try it. The regular 1/4" FastON tabs are the primary connection mode. these are nice and cheap and work well as a surface-mount connector, and you can pick up crimp-on female connectors cheap from any hardware / automotive store in every cable size. The Hadron shows some extra power connectors on the front edge, but those are for 5V only and wont be installed.
On detail missing in these renderings is the connector for thermistor /LED control, which will probably be a regular right-angle 4-pin 0.1" header, surface-mount-style.
I would have liked to use screw terminals or such but since all connectors will eventually be on the underside of the board, that would require taller standoffs, and those are more expensive anyways. if you have any opinion on this its not too late to change that.