Hello all. This is my first post on this forum and I'm looking for some help with a project. I'm a real novice so I'm sure this will be an easy one for the assembled minds.
I'm trying to build a replacement fuel gauge for a 1974 VW Camper. Originals are very fragile hot wire gauges so difficult to get hold of, and aftermarket replacements require me to cut holes in my dash. I can fit a 10-seg LED lightbar in the space utilising the old gauge casing to create a replacement in place of the original gauge.
The tank sender is a variable resistor ranging from 10Ω (full) to 75Ω (empty). I'm looking to display the output on a single 10-seg LED lightbar controlled by an LM3914 display driver. I'm using a fixed voltage regulator (TS78M06) and a voltage divider to provide the signal, but am limited by the current I'm prepared to put through the tank sender. This means I need to amplify and offset the signal before sending the length of the van, for which I planned to use an LM741 op-amp in negative feedback configuration. The circuit diagram is attached.
The problem, then, is with the op-amp. I've built the display part of the circuit, faking the signal voltage, and it works fine. I've built the transmit side of the circuit and it doesn't work. The voltages shown on the circuit are correct up until the Vsig output from the op-amp, which always saturates.
I'm sure this will be something simple, as I don't really understand electronics. I'm driven by necessity here rather than as a hobby, but I've got my teeth into it and don't want to be beaten now! Any ideas much appreciated.
I'm trying to build a replacement fuel gauge for a 1974 VW Camper. Originals are very fragile hot wire gauges so difficult to get hold of, and aftermarket replacements require me to cut holes in my dash. I can fit a 10-seg LED lightbar in the space utilising the old gauge casing to create a replacement in place of the original gauge.
The tank sender is a variable resistor ranging from 10Ω (full) to 75Ω (empty). I'm looking to display the output on a single 10-seg LED lightbar controlled by an LM3914 display driver. I'm using a fixed voltage regulator (TS78M06) and a voltage divider to provide the signal, but am limited by the current I'm prepared to put through the tank sender. This means I need to amplify and offset the signal before sending the length of the van, for which I planned to use an LM741 op-amp in negative feedback configuration. The circuit diagram is attached.
The problem, then, is with the op-amp. I've built the display part of the circuit, faking the signal voltage, and it works fine. I've built the transmit side of the circuit and it doesn't work. The voltages shown on the circuit are correct up until the Vsig output from the op-amp, which always saturates.
I'm sure this will be something simple, as I don't really understand electronics. I'm driven by necessity here rather than as a hobby, but I've got my teeth into it and don't want to be beaten now! Any ideas much appreciated.