Like many things on Tindie, it contains a building block that others can expand on and use in their projects.
Apparently yes, but that doesn't mean that everybody SHOULD add carelessly designed stuff on top of it ...
My comments:
ATTiny can sink/source 40mA, the coils in the Switec are 20mA. Should be fine; despite your concerns
Sure enough. It is your project. Do whatever you like. And in general I don't have any concerns ... why should I? - it's not my project. I just try to help you by challenging some aspects. If you come to the conclusion that it will work nevertheless it's fine. But I assumed that you placed it here to get some feedback. Or was it just or advertising???
If someone wants to add a simple diode & fuse; on the front end, they're welcome to.
But I don't see any design files for the PCB published. So how would somebody contribute? Maybe I'm just too stupid to look but otherwise these types of problems are common with half opened projects :-(
I mean seriously - why won't you share your design files?
BTW, here is a thread on automotive input protection
https://www.eevblog.com/forum/projects/automotive-device-power-supply-design-do-i-need-tvs-and-resistors/ As for the 'horrible' layout of the Vcc and Gnd, I wouldn't mind hearing your explanation; or were you just having a bad day?
They're already 20mil, kept well away from other things, and relatively straight from the connector through to the uC. Admittedly it does jump through the board at the decoupling cap, but I'll change that on the next rev of the board.
Well, the first thing is that I ASSUME (based on the ground trace from the decoupling cap to the ISP connector) that you don't have a ground plane. Between VCC and GND you have quite large loop areas so this thing will be problematic EMC wise. It will radiate quite a bit and also be be more sensitive to EM radiation from the outside.
I would suggest to pour ground planes on BOTH sides and stitch them together with a lot of vias. Ideally you would not cut the ground plane on the bottom side - if necessary cover the area with ground on the top layer. I would place the positive pin of the decoupling cap even closer to the VCC pin on the ATiny.
See a fantastic example in the design files published here:
https://www.eevblog.com/forum/projects/isp-mini-yet-another-avr-programmer/ As for the regulator - please read the datasheet (i.e.
https://www.fairchildsemi.com/datasheets/MC/MC78L05A.pdf):
1) Capacitor on the input is required.
2) Also the regulator is quite on the edge of specification power wise. In a car environment it has to drop 13.8V-5V = 8.8V (under good conditions- could be worse though). Given 40mA of your two coils and the losses in the rest of the thing, it would be safe to assume a need of around 50mA. Hence the regulator dissipates 0.44W of heat. Given the thermal resistance of 150°K/W the junction-temperature will be at least 66°K above ambient. So there is not that much margin on a hot day ...
Further, you could source the stepper with a higher voltage, too. According to the datasheet (
http://www.jukenswisstech.com/JSTFiles/downloads/2011/06/X27_Flyer_v1.3.pdf), the coils are rated up to 9V. Of course you would design the driver to source that 20mA when holding the position. But when changing the magnetic fields in the stepper, the higher voltage comes handy to build up the field more quickly. Initially you would have 0mA current flowing due to induction. Hence especially when moving quickly this might be necessary to not loose steps.