Fuel Gauge/Sender Variants

[bigbadbob76]

Ok. So the mk3 version works well.
Pin sharp response and built in hysteresis and turn on delay to reduce bounce, at the expense of a slightly more complicated circuit.
I can't do anything about it coming on when you go up and down hills though. Thats just the laws of physics Capt'n.

LED off.


LED still off.


And 3 seconds later-





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[bigbadbob76]

Here's the circuit diagram.
Don't change the values.
Vr1 set about half way for 7.5V trigger.

[CJH]

Great stuff - I'll see how many of those components I've got already. I definitely don't have an MC3423! It looks as though it will still fit onto the back of the fuel gauge, with connections off to the LED circuit and GND, just like MK2.

[bigbadbob76]

Vr1 set about half way for 7.5V trigger.

I tell a lie, it's closer to the top of VR1, 2470 ohms.

It might mount on the back of the gauge but it would sit beautifully on a MK2 luxury version of your dash PCB along with our shift light.

I can send you a couple of the chips if you want.

[bigbadbob76]

Mk2 fitted. I'll have to let the fuel level drop now and see what the bounce is like.

[CJH]

It might mount on the back of the gauge but it would sit beautifully on a MK2 luxury version of your dash PCB along with our shift light.

I can send you a couple of the chips if you want.

Haha - well I didn't want to assume anything regarding IP, but if you'll allow it then I'll certainly see if I can squeeze the extra components onto the PCB, if and when I need to order another batch. But of course a separate gauge-mounted board would be good for any 'early adopters' of the dash PCB who might want to retro-fit a fuel warning light, or in fact anyone else who wants to add the warning light to their existing setup. I could make a bespoke PCB and have them made at very little cost the next time I'm ordering other PCBs.

Thanks for the offer of the chips, but since I'll need to order in some components anyway I might as well add some of them to the order.

[bigbadbob76]

Hadn't thought about IP.
I guess it remains with me and I'm happy for anyone to use my designs published on the Club 80-90 forum for non commercial purposes.
I also herby permit Chris CJH and only Chris CJH to use my designs published on said forum, and those I send hem privately, for his commercial purposes on condition he sends me, upon request, one blank unpopulated board of any PCB's incorporating my designs he sells for commercial purposes.
His experimental boards are exempt from this.

There you go Chris.
It's official, help yourself.

[CJH]

Woohoo - thank you! I guess if my commercial purposes were more, well, 'commercial', it might be different, but happy to be an exception under those terms!

[CJH]

First draft of an add-on board to implement Bob's Mk3 low fuel circuit. I shaped it to fit on the back of the fuel gauge in a 'non-tacho' cluster - I need to check that it'll also fit a tacho-specific fuel gauge.

[slowcoach]

Yesterday I finally found myself changing the tank. The issue of the fuel sender earth came up recently, not sure if it was thus thread or not? Anyway, it's true the sender earth is likely in a shocking state Like mine was...
I made a new one and coated it in chassis wax, hopefully that'll help things. But if the sender is using resistance values for its signal, this has to be a factor!
Chris I have a spare early ((I'll check that actually, I replaced it with a late one since my clocks are all late now) sender if you want one for any testing?

[CJH]

Chris I have a spare early ((I'll check that actually, I replaced it with a late one since my clocks are all late now) sender if you want one for any testing?

That's very kind of you, thank you. I'll see how I get on with in situ testing of my earlier sender, but that could be useful later, thank you.

I checked the fit of the PCB on a tacho backing plate - I don't have a genuine one so I used my reproduction, so there may be one or two mm difference. The PCB would probably have been OK, but I chopped the corners off so that it fits entirely within the outline of the backing plate. Had to shuffle the components a little.





Looking at photos online there seems to be a foil locating lug near the 10V connection (ignore all the arrows - it's not my photo), so I'll have to adjust the profile a bit to avoid that - much easier since I discovered that I can import a DXF file as an outline; drawing profiles in Eagle is 'clunky', whereas AutoCAD can get it spot-on. The exact position of the lug will be a bit of guesswork, but if I get it wrong then the board can always be lifted clear of the lug by using M4 nuts as spacers.

[bigbadbob76]

That little board looks good Chris, nice work.
Have you considered going down the surface mount route? It would leave most of the back of the board clear for ease of mounting.


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[CJH]

Have you considered going down the surface mount route? It would leave most of the back of the board clear for ease of mounting.

I haven't - I suspect that would be beyond my meagre soldering skills. I'll learn one day I guess. Maybe I could add a surface mount version of this board to the order to give me something to practice with.

I made another iteration of the through-hole board. I notched the profile a little to hopefully clear the foil locating lug, and I changed the capacitor footprint - after shopping for a 220uF capacitor I think a 6.3mm aluminium electrolytic will suit. Hopefully Bob will correct me if that's not right.

[937carrera]

Hi Guys

Just been looking in Bentley manual

doesn't say Ohms but says VW1301 tool value
pre 85 55 Full 560 Empty
Post 85 50 Full 320 Empty

Might be of use /might not

Rick

A few weeks late, but something I saw over on the Samba while trying to help itchy with his temp gauge was relevant here.

On the pre '85 vehicles the spec for empty is at the end of the reserve, post '85 the spec is given for the start of the reserve area, you have to look at the pictures as well as the text.

Back to arduino

[bigbadbob76]

I just checked my 220uF 16V electrolytic and it's 8.15mm diameter.
It might be worth having pads for a small capacitor between pin 2 and ground for ignition suppression in case of noise pickup, probably a 10nf or 22nf would be fine.
I don't know if we'll need it but would be a shame to get boards made and find out later we need it. and having the pads for it would be handy for experimenting.

Surface mount soldering is not too bad if you have a fine tipped iron you can do it manually.
Using physically larger sized resistors/capacitors helps, don't be tempted to use the tiny stuff at first until you get the hang of it.
A simple circuit like this is ideal for cutting your surface mount teeth on.