RVI Tachometer Conversion
Posted: Sat Jan 05, 2013 8:57 am
Seemingly in common with a lot of owners I have had issues with the performance of the RVI tachometer fitted to my +2 S130. It has the usual symptoms of jerky readings, suspect accuracy and this is in spite of renewing a lot of the old electronic components. Part of the issue is probably the tied up with using an Aldon ignition system which has a different characteristic than the old points arrangement. The Aldon system was fitted to the car when I bought it and performs with no problems at all, so no complaints there.
I spotted an article by Stuart King posted on the Internet Mini Encyclopaedia (http://www.ime.org.uk search for LM2917N)
in which he had replaced the original electronic circuitry with a modern circuit using the National Semiconductors LM2917N integrated circuit. The datasheet circuit had been amended to raise the meter current drive to suit the RVI movement by adding a couple of transistors and other components and resulted in a neat solution. This circuit picks up voltage pulses from the -ve connection of the coil and converts these to a current drive proportional to the pulse frequency.
The pcb layout was convieniently shown in the article and the board measures only 1" x 2.6" so will fit easily inside the RVI housing. In my case I mounted the board on two right angle brackets attached to the meter movement through two existing tapped holes. The only modification made to the RVI housing was to drill a hole in the side to enable access to the adjustment potentiometer.
The electrical wiring was relatively straight forward, the meter has two connections wired to the pcb and also needed is a 12volt supply, an earth and a signal connection. I utilised the existing 12volt and earth spade connections and made a new bullet connection for the signal wire.
I have included photographs below which show the construction and wiring details.
Whilst I had the tachometer in bits I also decided to sort out the internal lighting which in standard form in pretty weak. Trailing through the internet I found what I thought would be a neat solution courtesy of the model train world. In related sites on e-bay LED strip lights were advertised in various lengths which operated from 12volts.
The circumference of the tachometer housing is approx 300mm which happened to be the length of one of LED strips available. Not wishing to change the car wiring I terminated the LED wiring with the brass threaded portion of an MES bulb which would then screw directly into the existing lighting circuit.
The LED strip has a self adhesive backing and once positioned clear of any protrusions in the housing can be stuck into position around the meter movement behind the dial.
Again the LED installation is shown on the photgraphs below.
The tachometer operation on the bench is very good the only outstanding issue is to calibrate the meter in the car in its installed attitude otherwise there may be an error.
I am very pleased with the lighting circuit, it gives an clear even illumination which is not too bright, a big improvement over the original. I shall now look into converting other instruments lighting with an the LED strip.
I spotted an article by Stuart King posted on the Internet Mini Encyclopaedia (http://www.ime.org.uk search for LM2917N)
in which he had replaced the original electronic circuitry with a modern circuit using the National Semiconductors LM2917N integrated circuit. The datasheet circuit had been amended to raise the meter current drive to suit the RVI movement by adding a couple of transistors and other components and resulted in a neat solution. This circuit picks up voltage pulses from the -ve connection of the coil and converts these to a current drive proportional to the pulse frequency.
The pcb layout was convieniently shown in the article and the board measures only 1" x 2.6" so will fit easily inside the RVI housing. In my case I mounted the board on two right angle brackets attached to the meter movement through two existing tapped holes. The only modification made to the RVI housing was to drill a hole in the side to enable access to the adjustment potentiometer.
The electrical wiring was relatively straight forward, the meter has two connections wired to the pcb and also needed is a 12volt supply, an earth and a signal connection. I utilised the existing 12volt and earth spade connections and made a new bullet connection for the signal wire.
I have included photographs below which show the construction and wiring details.
Whilst I had the tachometer in bits I also decided to sort out the internal lighting which in standard form in pretty weak. Trailing through the internet I found what I thought would be a neat solution courtesy of the model train world. In related sites on e-bay LED strip lights were advertised in various lengths which operated from 12volts.
The circumference of the tachometer housing is approx 300mm which happened to be the length of one of LED strips available. Not wishing to change the car wiring I terminated the LED wiring with the brass threaded portion of an MES bulb which would then screw directly into the existing lighting circuit.
The LED strip has a self adhesive backing and once positioned clear of any protrusions in the housing can be stuck into position around the meter movement behind the dial.
Again the LED installation is shown on the photgraphs below.
The tachometer operation on the bench is very good the only outstanding issue is to calibrate the meter in the car in its installed attitude otherwise there may be an error.
I am very pleased with the lighting circuit, it gives an clear even illumination which is not too bright, a big improvement over the original. I shall now look into converting other instruments lighting with an the LED strip.