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MG Midget and Sprite Technical - NMC. RPM warning light system

Are there any electrickery people here?

On the old 1920s/1930s Austin Seven engines they have a nasty habit of divesting themselves of crankshaft journals if the engine is permitted to wallow in the 2200 to 2400 rpm band for very long. I was wondering if some kind soul could suggest a method of making a simple warning 'gadget' to light up a bulb if the car sat in that band of speeds. Is it a simple job or would it take some expensive kit to make? It runs points via a Lucas distributor system so is quite similar to the Spridget although some are still 6 volt.

I'm a bit of a dunce on anything utilising electrons, a bit like Mr Lucas was.

Ta

Rob
r thomas

Fit one of these?

http://www.ebay.co.uk/itm/4-Digital-Red-LED-Tachometer-RPM-Speed-Meter-Hall-Proximity-Switch-Sensor-NPN-/261324169832?_trksid=p2054897.l4275
Lawrence Slater

Ah, but it needs to announce that you are sitting within that vibration band. I could fit a revcounter but it would need to make it known when the car was between those 2 RPM speeds. Even something with a shift light would only tell you that you'd reached the first speed but would then stay illuminated once you had exceeded the higher figure.
I'm not savvy enough to know if this is unworkable.
r thomas

Rob,

Here is an idea for you that might make a good basis http://homemadecircuitsandschematics.blogspot.co.uk/2013/05/make-this-car-over-speed-limit-warning.html .

You would require 2 of those circuits, one for the lower limit and one for the upper. I think fitting a bulb or buzzer or whatever suitable indicator between the output on each circuit , pin 3, would only power it when in the band you have set for the upper and lower RPM as outside that range the output signals would be at the same level and so no current flow.

For the input signal I would try the CB contact on the coil as when the CB is open the coil will pull the signal to 12V and down to 0V when closed.

I know you said you were not good with electrons but that circuit is basic and simple and uses cheap parts. It could easily be prototyped on a plug board or VERO fairly cheaply.

Plenty of cheap shift lights on ebay but without buying one and gutting it to see how it works and if it can be modified to combine 2 for a single indicator no idea if it would work. Would 2 shift lights be acceptable, neither on below bad RPM range, 1 on bad in bad RPM range, 2 on good above bad RPM range assuming the RPMs suitably set.
David Billington

Why not just a tach... I stare at mine constantly

Prop
Prop and the Blackhole Midget

Eeeeek! Cable brakes, non-synchro gearbox, no doors, no safety belt or airbags....I can't envisage me spending much time looking at a Tacho!!!

Anyway, whilst a Tacho MIGHT give the required data it wouldn't ALERT me to having the engine in the danger band. Even a shift light would only tell me that I had passed the lower edge of the band without telling if the engine was now above it. Most of the obvious options are quite what I'm looking for and now that I'm able to devote time to tinkering I'd like to find a solution that works just the way I want it and then if it can be made simple and cheap I can make a few more for other enthusiasts.

I followed the link David posted and it brought me to a few other options. Best avenue so far seems to be a LM2907-N chip and a home-made board. The expertise needed to design the board is beyond me but I'll look around for a knowledgeable electronics expert.

Oh, and there is no requirement for the car to have any instruments at all so I'll only be fitting an oil pressure gauge to the dash, nothing more. :o)



Pic of the bulkhead/dashboard--->

r thomas

The LM2907-N sounds like a useful piece of kit.

It might be worth emailing the guy at the 'homemadecircuits...' website and see if he could come up with something. He seems to be quite helpful.
Dave O'Neill 2

Rob,

The circuit I liked to has a 555 timer configured as a frequency to voltage converter but if you go the 2907 route then have a look at some of the application notes such as http://www.jameco.com/Jameco/Products/ProdDS/23317.pdf . National Semiconductor always seem to have a pretty good set of application notes and that data sheet contains items such as the voltage driven meter on page 9. Add a pair of voltage comparators on the output voltage with suitable potential dividers to set your critical speed points and driving an indicator should be simple.
David Billington

Some progress.

It should also be capable of monitoring oil temp, oil pressure and water temp via some cheap sensors.

r thomas

I was too thinking that the Arduino would be a very suitable platform to achieve your aim. It would be comparatively simple to program it to produce a warning light in specific rev range(s). You could further make it so (for example) an amber light comes on when you first enter the rev range but turns red if you stay within that range for more than say 20 seconds. Very customisable. It need not look quite as complex as your photo implies.
Jim
J Smith

I can't claim credit for it. So far all the heavy thinking has been done by Andy the electric guy in Gloucester.
The further it goes, the more clever ideas come out. Latest gadget is a revcounter calibration tool made with a hall-effect kit and an electric drill. You can vary the drill speed and more easily measure the drill chuck speed.

r thomas

This thread was discussed between 27/12/2014 and 06/01/2015

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