ok ive got a fj40 landcruiser thats now on straight lpg they want 200bux for the converter to use the standard gauge with the lpg tank so i said stuff that
anyway the lpg sender is 0 ohm empty and 90 ohm full and the standard gauge is 120ohm empty and 17 ohm full
so what im wanting is a simple circuit so i can hook them up and have a proper gauge
i can build circuit boards and stuff im just no good ad designing circuits i just dont know where to start
I can't think of a passive design that will do this (off the top of my head). there could be one ??
an easy way of doing it is using an inverting amplifer design. but you would have to work with voltage/current references not resistances. that's easy to do, but you need to find out a little bit more about the electrical characteristics of the fuel meter.
here is one way i would do it (basic overview)--
- i would supply the tank a constant current, say with a current mirror (you can configure an LM317 as a constant current source). that would give you a resistance to voltage conversion.
- feed this voltage into an inverting opamp configuration. This will produce an inverted voltage.
- What you do with the output voltage (or current) depends on how the fuel meter guage works. you might find that the meter is measuring current flow for example. if so, then you can configure the opamp to supply a given current.
me personally, if you are not prepared for a few days of analysis, building, testing etc.. then i would just pay the 200 moola. alot of time and energy goes into designing something that reliable and ruggled. $200 sounds like a cheaper opinion.
i would try to build it though, it is sounds like a fun project ;)
Maybe I am dreaming but the solution seems simple to me - just install a switch that changes the input to the fuel gauge from the petrol sender to the lpg sender, BUT include a 18 ohm (or so) resister in the lead from the lpg sender.
Note that the full to empty range of both senders is fairly close, but that the lpg sender empty is 0 whereas the petrol empty is 17ohms. So if you just compensate for this initial resistance you should have a near enough gauge for your lpg. Remembering that fuel gauges only provide a rough idea of fuel capacity, this should be near enough and certainly better than spending $200 for ???
And put 360Ohms across the meter to bring the full-scale resistance correct. You could be pedantic and put it across the series resistor as well, but it's close enough either way.
Ken
"quietguy" wrote in message news: snipped-for-privacy@REMOVE-TO-REPLYconfidential-counselling.com...
And don't forget a new scale on the guage as the sender operation is now reversed (ie fuel giage says full when it is actually empty!)
Alan
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