Motherchip
The motherchip talks ieee 1284 protocol with the EPP parallel port, receiving control commands, motor torque commands, and receiving position, state, home offset, and general i/o. The ieee 1284 protocol has some rather tight timing requirements (must pull ack low within 10usec of data strobe) so it handles comms while the attiny13's in the iskewb are busy counting encoders. The motherchip has 8 (expandable!) slave select lines to talk to 8 iskewb's or other peripherals. Maybe will throw in some kind of power supply monitoring as well..
Should be able to squeeze it into a tiny card, but will fit into half a 1U rack slot if nothing else..
Parts:
- atmega48 microcontroller
- talks to a PC or thin-client (such as the netier xl1000 running emc2 via the ieee1284 protocol across a standard EPP parallel port, handles a small amount of I/O, and drives the SPI bus to control each individual iskewb
- ps2505-4 quad photocoupler, qty 4
- to protect the computer and parallel port from voltage surges and protect the motherchip from static discharge during handling - cheap insurance, Jameco P/N 320725 $1.29 each min qty 1 -- might be too slow, rise time 5us fall time 3us
- HCPL2530 2 channel high speed opto .4us rise time .4-1.5us propagation delay Digi-Key $1.94 ea
- tlp2630 2 channel high speed opto 0.03us rise time 0.075us propagation delay, note: inverts the output digi-key $2.25 ea
- 4n33 Opto Isolator qty 8(?)
- t- goldmine-elec.com p/n G13385, $0.20 each min qty 5
- pcb mount RJ45 jack qty 8
- side entry low profile Jameco P/N 524461 $0.55 ea min qty 10
- OR
- ES1607 shielded PCB mount RJ45 jack from excesssolutions.com $0.25 each min qty ??
