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CyberJacket MkII: The Nine-Wire Bus - Initial Thoughts

Why 'Nine Wire'?
D Type 10 Pin Header Label
Function
 
1 1 RQONOFF 0v - wake; open/+v - sleep Controlled by sensor driver modules
2 3 Rx1 RS232 Rx for general purpose use For ad-hoc connection of RS232 devices without driver modules
3 5 Tx1 RS232 Tx for general purpose use (as 2 above)
4 7 +V Unregulated +V supply - 7 to 17v Regulated supplies are generated from this line using voltage convertors/regulators as appropriate at each device. Devices are switched on/off by local controllers. 
5 9 Gnd Ground -0v  
6 2 Gnd/Spare Ground for 'mirror' RS232 working with Rx3/Tx3 See also 8 & 9
7 4 Tx3 Serial Tx connection to sensor modules Sends requests for data to all sensors - $S"%s"xxx..x (%s: sensor name xx..x: data threshold)  4800 baud (3.3V CMOS?)
8 6 Tx2 RS232 Rx for connection to Handheld/Palmtop display  Generally used as an output port - N.B.This connection will function as a conventional RS232 port when a conventional RS232 connector e.g.'D' type is connected the 'wrong' way round onto the bus (but make sure the unused pins are cut/disconnected).
9 8 Rx2 RS232 Tx for connection to Handheld/Palmtop display As 8 above
NC 10 Rx3 Serial Rx connection to sensor modules Receives data sent from sensor modules - $R"%s"xxx..x 4800 baud TTL (3.3V CMOS?)(as 7 above)

OK - it's really 10 wire - but two are connected to ground! Inspired by Spinal Tap!!

Conventional 10pin IDC headers are capable of being connected to two ribbon cables simultaneously and hence can provide 'Y' junctions on the bus n.b. substantial clamping pressure is required to ensure proper contact is made. .

We have tested standard 'grey' ribbon cable - it has a resistance of 0.16 ohms per metre. At 1.5 amps the voltage drop across one metre is 0.25v. A current of 4 Amps was successfully passed through it without catastrophic failure (it did warm up a bit though!). We conclude that it is suitable for use on our wearable with the Bitsy and multiple sensors. However the use of head mounted, or other, displays will probably require dedicated power supplies.

In addition USB and audio in/out are available. Relevant devices can be connected directly to the processor board.
 


This page last updated July 18, 2002
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