Don't Jinx it!!! :icon_eek:

:)

Tried constructing the low fuel light today on a breadboard. I've checked it, double checked it, triple checked it and completely re-built the bloody thing, and it does nothing. Apart from turning the light on continually, regardless of the settings on the pots, or the simulated fuel level set via a potentiometer standing in for the fuel sender. Bah! :(

Anyhow, I've done some more googling on the subject and found this:

http://www.fizzindi.demon.co.uk/MX-5...ng%20Light.doc

Which seems a much more in depth, step by step guide to making a low fuel light with a comparator. I think I'll be stopping off at Maplin again tomorrow. :)

In other news, I've found a decent welder who's coming to weld the harness turning bar in now I've cut and notched the tube, and I've filled all the dings in the fibreglass. The cockpit floor, tunnel and firewalls have been covered in sound deadening material, and I've installed the trim rings for the handbrake and gearstick (rivnuts into the top of the tunnel, stainless fixings).

Once the weldings'd done, and the tub has been sanded smooth again, I'll get on and fit the carpet.

Full speed ahead! (Until I run out of fuel because the bloody warning light doesn't work! :D)

Hi Jason

If designed properly (IE well damped so you get an average reading over several seconds) I'm beggining to think that a warning light may be better than the gauge. On my car it wangs arround all over the place - a symptom of no baffles in the tank methinks.

Looking at the circuit diagram you posted I am not sure that it will be very good. For a start just putting a zener diode accross the supply without any in-line resistance is not the best of idea's. The biggest problem of car electronics design is the horrible noise and variations you get on the power supply. I am no expert nowadays (20 years since I did any serious electronic design) but I would suggest you at least need to stabalise the supply to the comparator. Anyone else agree/disagree?

Robin

I'm sure you're right, Robin - but I wouldn't know, as I know nothing about this sort of thing! The last time I did any circuit design was back at school. :)

I'm just wanting comprehensive instructions for something that will work, that I can bung together on strip-board.

Any better?

http://www.westol.com/~beaurega/gas.htm

I thnk both designs are essential the same, but the MX5 one does incorporate a capacitor which should smooth the output.
I must say my gauge would go from full to empty under cornering or acceleration, so I may well be trying the same thing later.

OK. A couple of small mods I would do then.

1. Put a low value resistor (say 10 ohms) in the +ve supply line. This should limit the power that the 15v zenor sinks in the case of a big voltage spike. probably should be rated at about 1 watt
2. Put a largish electrolytic capacitor in parallel with the zenor - say 100 uF. This will help to absorb any voltage spikes.

A up to date electronics man might suggest something more sophisticated - but I would at least do that.

Robin

Thanks Robin - I'll breadboard it at some point during the weekend to see how it goes, and drop in the mods you suggested.

My mate Rob (the OCD ex electronics engineer) has just popped by my desk with a new circuit he's come up with, using an LM2903 dual comparator - I'd post the diagram, but it's hand drawn and needs transcribing - but the gist of it is that it has hysterisis built in, has a 9V regulator to smooth out the power and has an adjustable "on delay" to help with the sloshing of fuel under cornering, acceleration and braking.

It's also tailored to the fuel sender I have (an ETB one, which registers full at 14R and empty at 264R).

I'm waiting for him to come back from lunch to discuss it more (it's a quiet day) and get a few more details. It looks very thorough! :)

In other news - the welder is coming tommorow morning to weld my bar in, and I've filled all the dings in the tub, and rubbed them back. Hopefully I can have the back end re-assembled on Sunday, ready for another viewing. Marlin mentioned to a chap in Brixworth that I was building a Sportster, and he wants to come and have a chat.

Well, the bar has been welded in now, and painted up. I'll post some pics of it tonight, but I think it looks pretty smart. You swouldn't know it hadn't been there all the time - Thanks for pointing me in the right direction on this guys. :D

Pics of the seatbelt bar:

http://www.greatoldone.co.uk/Sportst...atbeltbar1.jpg

Join? what join? :D

http://www.greatoldone.co.uk/Sportst...atbeltbar2.jpg

http://www.greatoldone.co.uk/Sportst...atbeltbar3.jpg

And knock me down with a feather and other exclamations of joy and amazement - My bumpers have arrived! :)

Fronts:

http://www.greatoldone.co.uk/Sportst...ontbumper2.jpg

http://www.greatoldone.co.uk/Sportst...ontbumper3.jpg

Rear:

http://www.greatoldone.co.uk/Sportst...earbumper2.jpg

http://www.greatoldone.co.uk/Sportst...earbumper3.jpg

They look slightly different to your bumpers - they have 'bumps' at the end. I assume that these are there to ensure that they meet the IVA requirement of having the bumpers a certain distance from the body work at each end.

I also assume that they'll pass, as Terry made mention that Mark had took copies of them to the Exeter test station to get them checked before making up mine and the another set for the other chap who's also been waiting for them.

How am I supposed to bolt them on by the way? I got a bag of self tappers with them - so I guess that's the Marlin method. What has everyone else done? I'm curious as to how you're supposed to locate and drill holes etc for the rear bumpers when the tubs on... Let me guess - I have to take the bloody thing off again?

And how far out should I be setting the fronts?

Welding looks really good there! Almost as if it was designed!

Yur are right about the ends of the bumpers. The IVA requires the ends to be turned in. My rears had only the outer ends turned in, and the IVA man gave them a cursory inspection.

On the cabrio the front bumper goes the whole way across, but the rears are split like the sportster. I assume the Sportster bumpers fit in the same way as the cabrio and the bracket goes into a tube and the outer part of the bracket is supposed to crush in an accident.
The cabrio did have a supporting stay at the rear, but the outside end was quite floppy and I could not get them to stay level. So when I had the rear tub off for painting I drilled and tapped a 5mm hole through the chassis rail and bumper bracket. I've assumed that if the worst came to the worst then the bolt will shear in an accident.

Without seeing your friend's circuit diagram (I'm making a guess here) although you know the resistance the ETB sender has the voltage across the fuel sender will depend on the internal resistance of the guage.
If you try to measure the resistance of the sender by passing current through it you will affect the reading of the guage.
BTW. the MX5 solution had some hysterisis in it as the 1Mohm resistor and big capacitor had a time constant of about 40 seconds when I did the sums

Yeah - the internal resistance of the guage is known as well - I measured them all before I gave the details to Rob.

For the curious, they are:

Sender ‘Full’ = 14 Ohms (It fluctuates a little, as the full movement is actually above the position of the top of the tank, so 20 Ohms from the sender FAQ is approx. correct)
Sender ‘Empty’ = 264 Ohms
Resistance across gauge = 142 Ohms

They look much better than the "original" ones. To fit mine I tapped an M6 thread in the chassis and a corresponding M6 hole in the bumper tube. You have to be carefull to get everything square though. Unless Mark has changed the tubes he uses, they will also need packing out or they will be very wobbly.

and yes - you will have to take the tub off again. Never mind - once you have taken it off about 50 times you get quite profficient at it...

Robin

Assuming at 12v supply you should see 1V when full and 7.8 when empty.

I'm not too sure you want to stabilise the power to the comparitor, If your reference point is truly fixed and your nominal 12v across the guage/sender varies it will cause the comparitor to toggle.

Thanks Guys - and I'll mention that to Rob when I see him next Chris. It'll make me sound as if I know what I'm doing! :dizzy: ;)

When fitting the bumpers for, hopefully, the last time I've put a squirt of silicone bathroom sealant inside the chassis rails to stop water ingress and to provide some packing.

I've updated my blog to reflect all the progress:

http://www.greatoldone.co.uk/Site/Bu...s_Update!.html

Lookin' great Jason. BTW - where did you get your gear knob and handbrake finisher from?

Robin

PS - I adopted your approach using a 3mm ally plate for the boot closure. Seems to work very well once you have got the hang of bending it!

I got them from europa -

https://www.europaspares.com/TRIM/TR...OUND_2448.html
https://www.europaspares.com/TRIM/TR...RO___2447.html

Yeah - I know what you mean on the ali front. "It's only aluminium" you tell your self. Several hours and much swearing later, you manage to get it to fit perfect on one side - only to find out your perfectly crafted bend on the other side is now out. :)