DIY Instrumentation

Technical discussion on converting internal combustion to electric
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4Springs
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Post by 4Springs »

I've been spending a bit of effort on the instrumentation in the Brumby, thought I'd write a summary.

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Here are a couple of views of the dash. There are a few additions here that a Brumby nut might notice:
1. The electric de-mister up by the windscreen. Otherwise known as a 12V hairdryer! Just about the minimum that you need to get through an inspection.
2. The Pre-Charge label and light. The light is one of those very bright blue LEDs, and is obvious even in sunlight. This light comes on and stays on until pre-charging is complete. Once it goes out you are ok to start the car. This label & light replace the previous label that said “lights” or something similar. Details about this are in my post “Simple Precharge Circuit”.
3. The slider on the left next to the windscreen wiper knob. This replaces the previous label that said “wipers” or something similar. The slider is an addition I made to provide an intermittent wiper mode – something we always missed when driving the Brumby! I'll make another post describing exactly how to do this in case anyone is interested.
4. The ammeter underneath the windscreen wiper knob. This is a re-purposed tachometer, and is driven by a Zeva Fuel Gauge Driver Plus (FGD+). More details in another post.

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Here is a closer view of the instrument cluster. From left to right:
- Clock, speedometer and odometer are not modified.
- The next bit is called the “teltale” in the manual. It tells the following tale:
We are in low range four wheel drive, the park brake is on, the right door is open, the lights are on but not on high beam. The “Rear Gate” is a re-purposed light that I use to say “your key is in the ON position but you have not yet started the car”. This light goes out when you turn to START. There is another light that I have re-purposed (well, actually I have purposed it, since it was not previously used), shown in the other photo as “EX.TEMP”. I have hooked this one into an over-temperature switch on the motor.
- The fuel gauge says that we are almost fully charged. This is driven by the FGD+ and works a treat.
- The temperature gauge is showing the motor temperature. Temperature gauges generally work on resistance, so I experimented to find the resistance range of my gauge. I then found a thermistor that gives that resistance over a range of about 0 to 100 degrees Celcius. So there is a thermistor stuck to the motor with epoxy resin, and another stuck to the controller. A small switch lets me select which one I want to view, although I find that the motor is the one that heats up first so I normally monitor that.
Last edited by 4Springs on Thu, 19 Feb 2015, 13:28, edited 1 time in total.
TooQik
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Post by TooQik »

Very nice! Quite a bit of customisation work there. Does the hair dryer turn on from the heater controls on the dash or does it use its normal switch?

Must say the "tell-tale" is a little worrying to look at when the power if off. Looks like someone is targeting the car. Image
Last edited by TooQik on Thu, 19 Feb 2015, 14:24, edited 1 time in total.
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4Springs
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Post by 4Springs »

TooQik wrote: Does the hair dryer turn on from the heater controls on the dash or does it use its normal switch?

I installed a switch on the dash. You have to know where it is though, definitely not obvious for someone who doesn't know the car. I'm slowly working on another heating method, so hopefully this is just temporary (3 years so far).
TooQik wrote: Must say the "tell-tale" is a little worrying to look at when the power if off. Looks like someone is targeting the car. Image

I've had someone in the car point that out to me once, they were very impressed by the long range scan...
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Post by 4Springs »

Adding an intermittent setting to your windscreen wipers.

Our newer cars have had an “intermittent” setting for the windscreen wipers. I've long thought that I could add one to the Brumby, and since I was going to replace the dash with a better one I decided now was the time. It turned out a bit more involved than I thought...

A picture of the finished result:

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The round switch is the standard wipers switch, and I've added the slider to its right. With the slider pushed left the wipers work as normal, but pushing the slider to the right provides a delay which increases in time from 0 up to about 30 seconds. This is only on the LO setting, the HI setting works as normal. There is a bit of space behind this section of the dash where I've hidden a small circuit board and a couple of relays.

To develop the circuit I first had to figure out how the wipers worked. I took out the switch but was quite confused. So I went a-googling and found this article which explains it nicely: Wiper Explanation
I came up with this circuit to provide the delay:

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The block on the left is meant to represent the plug to the wipers switch, and is drawn using the same numbers as in the article. So with the switch in the LO position 12V is connected through to wire number 3 in the diagram. Let's see if I can explain the circuit.

With the switch in the off position there is no 12V connected to the 12V rail.

When the switch is turned to LO, 12V is connected to position 3 on the WIPER box to the left. This provides a 12V rail for the 555 timer. The 555 is set up in astable mode, which means that the output pin 3 oscillates between high (12V) and low (GND).
- When low, the relay K2 is energised, which in turn provides 12V to the motor. This is the wiper motor, so the wipers operate exactly as they used to when set to LO.
- When high, the relay K2 is not energised, and the motor is not powered. If the motor was going when the 555 took its output high then the motor acts the same as if you had turned it off – it runs until it reaches its park position. I have illustrated this using a switch in the diagram. The Park Switch is at position 3 when parked, and at position 1 when not parked. So when the motor is running the park switch provides power to the motor through position 4 on the WIPER box.

There are two timings that we are interested in with the 555 oscillator. The first is the time that it spends with its output high. I've called this the off delay since the wipers are off. The off delay is set by R6, which in the Brumby is the slider that you adjust with your thumb.
The other is the on delay; this is the time that the 555 spends with its output low, and it is set by R7. This time needs to be shorter than a full circuit of the wipers. You'll know from experience that you can turn the wipers on and off again quite quickly to get one wipe. R7 is a trimpot which I set by trial and error to about 1 second.

The other part of the circuit is required because the 555 initially starts with its output high (wipers off). When you turn the wipers on you expect them to go – you don't want to wait that delay time. In addition the first cycle on a 555 in astable mode is slower than the subsequent ones. This is a property of the 555 astable circuit which I won't go into here. So anyway we need another circuit to provide an initial wipe when we are first powered up.
When we first get 12V the relay K1 will operate, pulling its switch in and energising K2 no matter what the 555 is doing. K1 will stay energised until C3 is charged. I chose the value of C3 to suit the small relay I had for K1 – it means that K1 stays on for about 1 second. This part of the circuit does nothing else once C3 is charged up, it is only there for the initial power-on. When power is removed the capacitor discharges through R2. Without R2 the capacitor might stay charged for a long time, meaning that the wipers might not operate immediately the next time they are turned on.

Here is a picture of the board, it is stuck on with double-sided tape. The relay K2 is the automotive relay held on with a screw. K1 is the long black thing on the board. C2 is composed of two 470uF capacitors in parallel. The slider potentiometer is behind the relay, not visible.

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Post by Johny »

Nice description Chris.
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4Springs
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Post by 4Springs »

Making an Ammeter
I purchased a Zeva Fuel Gauge Driver Plus (FGD+) way back when I first converted the Brumby. This instrument drives the fuel gauge, but also allows you to re-purpose a tachometer to read real-time Amps. An ammeter is very useful in giving the driver a feeling of how much power they are using to drive at this instant in time.
The Brumby didn't have a tachometer, so I bought an after-market gauge. The first one I came across was a digital one with bright blue numbers. The FGD+ provides a signal where 100 Amps is equivalent to 1000 rpm. So when my digital gauge read 2350 I was using 235 Amps.

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The digital gauge had a couple of drawbacks. The first one was the brightness of the thing. It was bright enough to be seen during the daytime, but could not be read in direct sunlight. At night time it was blinding. It was positioned quite low, and I didn't mind too much but the wife couldn't stand it. I had to come up with a cover to reduce the glare.

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This is a lid off a small jar that happened to be the right size. At night time you put the lid over the gauge – you couldn't read the gauge but you could see the road!
Another problem with the digital gauge was the scale. Reading 2304 to mean 230 is just not right! I'd rather a gauge that reads 1-10 and convert that to 1-10 hundred in my mind.

I decided to buy an analogue tacho to see how that would go. I went to a local shop and bought the only tacho they had. It was $35 and had a range of 0 – 10,000 rpm. When I thought about this some more, and realised that I spend most of my time below 200 Amps I decided maybe I needed something with a smaller range. I normally use around 100 – 250 Amps, but can occasionally go up to 500. My controller could probably push more into the motor but I'm a bit afraid to try that as something might break! So I looked on-line for a tacho with a more reasonable range of 0 – 6000, but they are much less common, more expensive, and the gauge didn't travel as far around as the one I had bought, so really they weren't much different. I decided to see if I could change the range of my 0 – 10,000 rpm gauge.
Tachometers measure the number of pulses on their input wire. This is different for different engines. So the FGD+ is configurable for different engine sizes – 2 cylinder, 4, 6 or 8. The gauge is also configurable – 4, 6 or 8 cylinder. It turns out that tachos expect 4 pulses per revolution for an 8 cylinder engine, 3 per rev for a 6 cylinder etc. So by changing the configuration of both the FGD+ and the tacho, I could change the distance that the needle moved on the face of the gauge. This would be terrible if I used the existing face, but if I could make my own with new numbers...
Looking at the gauge face, I decided that it would be good if I had 600 A where 9,000 rpm was. This was tricky to work out, but I figured out that it would work with the FGD+ set to 6 cylinder mode and the gauge set to 4 cylinder mode. How does this work? Well I wanted the gauge to see 9 when the FGD+ sent 6. Set on 6 cylinder mode, the FGD+ sends 3 pulses per rev. For 6 rpm this means 6 x 3 = 18 pulses. With the gauge in 4 cylinder mode it expects 2 pulses per revolution, so 18 / 2 = 9. Great! Now I need to make a new face for the gauge.

At only $35 I wasn't too concerned about accidentally wrecking the gague. I found that the glass face is crimped around the edge. I managed to prise it off eventually by working all the way around with a small screwdriver. Once the glass is removed the gauge hand can be prised off. The face then falls away exposing the electronics underneath. So all I need to do is to make another face, this one with the numbers at the spacing I want.
The 10 (000 rpm) happens to be at 270 degrees from the 0. My new scale is 2/3 of the old one, so 10 now becomes 6.667 A. With that information I can write a formula to give me exactly where each number should be (in degrees rotation from the 0 at the bottom):
degrees = 270/(6.667/Amps)
So for example 2 (00 Amps) will be at 270/(6.667/2) = 81 degrees
I found a drawing program (LibreOffice Draw) that would let me draw lines and then rotate them an exact number of degrees. Once I had drawn a few I could then copy, paste and rotate to get the rest. I decided to colour everything above 500 Amps red, to give people the idea that this is pushing it!

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I printed out a test copy, glued it to some cardboard and inserted into the gauge. I ran the digital tacho next to the new analogue one while my wife was driving to see how they compared. It was great! The analogue one has a much nicer response. The digital gauge displays the number for a half a second or so before updating to the next number. So there is always a delay to let you read it. The analogue one has no delay, the needle goes up and down as your foot goes down and up on the accelerator.
The cardboard was good as a test, but I'd like the back-lighting to work. This gauge has multiple LEDs of different colours behind the face. There is a button to press that lets you select the colour. The white and red lines are translucent while the black face is opaque. So I took my drawing along to a local sign maker. For $25 they produced a vinyl sticker (shown above) which they stuck to clear plastic. The result is quite acceptable, it would be better if it was matt (it is a bit shiny), and if the black was opaquer, but it is fine.

There is a feature of this gauge which needs some explaining. When first turned on, the gauge runs all the way to the end (10,000 rpm or 270 degrees) and then back to zero. This is all well and good, except that if it starts out at some other point it thinks that is zero. So when I was charging my car the ammeter was reading about 15 Amps or so. The gauge is only powered with the key in the ON position. When I turned the key off the gauge stayed at 15 A. When I turned it on again it decided that this was zero. It moved all the way through 270 degrees, returned to zero (15 A) and then moved 15 A further along. So every time I turned the key off and on again it moved a bit further around!
I figured out that I could tell it where full scale was by planting something in the way. So if I put my finger in the way on the dial, when it first starts up it runs around there, bumps into my finger and stops. It then returns back 270 degrees from that position and calls that zero, no matter where it actually started from. Installing a mechanical stop at 270 degrees from 0 then ensures that the zero is reset each time the gauge is turned on. I used a thumbtack, the shadow of which is slightly visible when the gauge is lit up.

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The backlighting for this gauge is also very bright, but being able to select the different colours is a bonus. I imagine we'll have it set on red to not ruin our night vision. This gauge has a separate wire to supply the backlighting. I had hoped to connect this to the dash light dimmer dial but no joy. The original lights in the dash are provided with 12V, and the dimmer dial inserts a resistance into the earth return. The gauge has a common earth (for gauge operation and backlighting) so this wouldn't work.
I did some experimenting with resistors in the 12V line to reduce the voltage to the gauge backlighting. I found that 500 ohms was about the limit, any more than that and the LEDs flickered. So I have put a 500 ohm resistor in that line, and will probably put in a switch sometime so that the backlighting can be turned off. Another option is that I could put a variable resistor that allows the driver to adjust the brightness, but personally I find that I set those once and never touch them again. I'll see how it goes.

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