Thanks to all for your comments.
The parts cost is less than £15 including PCB. Assembling it in the UK would be uneconomic because of the large number of through-hole parts (i.e. the connectors), so it would have to be assembled in China. I'll get some quotations when the Chinese New Year is over. The initial selling price I had in mind was about £35, but if the production volume became high enough then sub-£30 + shipping + tax (where applicable) should be achievable.
Regarding LCD displays, my intention was to be able to drive a 12864 display and rotary encoder directly from pins on the expansion connector, with 5V signal levels for the 12864. I have a driver for the 12864 that supports proportionally-spaced text and uses a 1K image buffer. The mcu could DMA from the image buffer to the 12864 on a regular basis, to keep the load on the mcu low.
I chose series wiring for Z motors instead of parallel wiring for a few reasons:
* It is more appropriate in most cases, assuming the Z steppers are the same sort as the X and Y steppers (and therefore need about the same current) and are reasonably-well matched to the drivers.
* Novices can generally manage to wire stepper motors in parallel, but don't know how to wire them in series
* If the option of software-controlled stepper motor current is used, then the XYZ steppers will all get the same current; so if they are the same types of motor, series wiring is again more appropriate.
I've chosen screw terminals for the power and heater connections, but not for the others. A lot of controller boards are sold in kits, and the wiring of a kit is simpler if the looms just plug into the board.
I don't plan to support an ATX power connector, because IMO this is better done on a separate board that also provides resistors to give the minimum load needed on the 5V and 12V rails (as RepRapPro did on the Ormerod 1). Such a board could also include a diode for implementing the PS_ON facility, using one of the expansion header pins. However, I would provide a dedicated PS_ON output if the demand is there.
Regarding thermocouple inputs, I don't think they belong on a budget board like this. It would be easy enough to connect a thermocouple amplifier board to the expansion connector. On-board thermocouple amplifiers might be a good addition to higher-end boards, such as the Duet and Smoothie.
Quote
dougal1957
I think you could be on to a winner with this idea especially if you can get the price break to be similar to that of a Mega + Ramps combo and that seems to be around the £25-30 mark (suspect this may be the stumbling block).
The parts cost is less than £15 including PCB. Assembling it in the UK would be uneconomic because of the large number of through-hole parts (i.e. the connectors), so it would have to be assembled in China. I'll get some quotations when the Chinese New Year is over. The initial selling price I had in mind was about £35, but if the production volume became high enough then sub-£30 + shipping + tax (where applicable) should be achievable.
Regarding LCD displays, my intention was to be able to drive a 12864 display and rotary encoder directly from pins on the expansion connector, with 5V signal levels for the 12864. I have a driver for the 12864 that supports proportionally-spaced text and uses a 1K image buffer. The mcu could DMA from the image buffer to the 12864 on a regular basis, to keep the load on the mcu low.
I chose series wiring for Z motors instead of parallel wiring for a few reasons:
* It is more appropriate in most cases, assuming the Z steppers are the same sort as the X and Y steppers (and therefore need about the same current) and are reasonably-well matched to the drivers.
* Novices can generally manage to wire stepper motors in parallel, but don't know how to wire them in series
* If the option of software-controlled stepper motor current is used, then the XYZ steppers will all get the same current; so if they are the same types of motor, series wiring is again more appropriate.
I've chosen screw terminals for the power and heater connections, but not for the others. A lot of controller boards are sold in kits, and the wiring of a kit is simpler if the looms just plug into the board.
I don't plan to support an ATX power connector, because IMO this is better done on a separate board that also provides resistors to give the minimum load needed on the 5V and 12V rails (as RepRapPro did on the Ormerod 1). Such a board could also include a diode for implementing the PS_ON facility, using one of the expansion header pins. However, I would provide a dedicated PS_ON output if the demand is there.
Regarding thermocouple inputs, I don't think they belong on a budget board like this. It would be easy enough to connect a thermocouple amplifier board to the expansion connector. On-board thermocouple amplifiers might be a good addition to higher-end boards, such as the Duet and Smoothie.
