Date   : Sun, 21 Nov 2010 18:42:56 +0100
From   : rick@... (Rick Murray)
Subject: Using a Beeb for engine monitoring

On 21/11/2010 18:20, Alex Taylor wrote:

> chokes, points ignition and so on. I've often wondered if such things
> as universal fuel flow and speed sensors can be bought separately, in
> order to create a trip computer with a realtime MPG readout.

Apparently my father, back in the late '70s, fitted into his car about 
every single dial and monitor available. Mom says it looked quite 
ridiculous. ;-)


> I'd want to create this using one of Sprow's MiniBs, linked to a
> serial-port LCD display.

Question is, would the MiniB cope? I would imagine a *lot* of it is 
highly analogue, like rheostat (or worse, fluid-filled-bubble) 
temperature sensing. Or tach/odo working by essentially having a 
spinning disc with a magnet dragging a disc hooked to a spring. You 
might be able to rig up some sort of sensor like a Hall Effect 
(cannibalise an old floppy drive?) but how fast does that disc actually 
turn? Would the interrupt handler be up to the job? I can't imagine the 
tach is a flat 1:1 from the engine (giving a range of around 800rpm idle 
to 6-8000 red lining it), but if it is... 3000 is 50Hz, this 6000 is 
100Hz. There ought to be wiggle room there, it depends on what else 
you'll be sensing at the same time, and the calculation speed... plus if 
IRQs are disabled while writing a log. That said, as you are only 
"looking" at the car, not controlling it, you could easily suspend 
monitoring for a second at a time with no big effects.

I've just Googled Sprow's MiniB and it doesn't have an ADC. Mmm... It 
does appear to have a 1MHz bus, so you ought to be able to hang a few 
ADCs off of it. You ought to be able to do better than the ?7001 - 
perhaps a nice fast ADC with more inputs?

I think the question, for the moment, will come down to:

   What do you want it to tell you?

Which will determine what sort of things you will need to monitor, which 
will determine what sort of hardware you will be looking at.


Best wishes,

Rick.

-- 
Rick Murray, eeePC901 & ADSL WiFI'd into it, all ETLAs!
BBC B: DNFS, 2 x 5.25" floppies, EPROM prog, Acorn TTX
E01S FileStore, A3000/A5000/RiscPC/various PCs/blahblah...