Project: Display of Speedometer/Odometer + Battery Info

[Wingsy]

I’m about to undertake a project to outfit my 2003 DS Club Car with a speedometer/odometer and battery charge/discharge status. This post describes what I’m planning to do, and I’m here to ask for any suggestions anyone might have.

The display is a lighted 2-line LCD, with 16 characters per line. I’ll be mounting it in the dash, with 2 pushbuttons in the back of the display for calibration. See the attached PDF, showing the displayed items when not charging (at the top) and when connected to the charger (at the bottom).

When the switch is on, and for 5 minutes after being switched off, the display will show speed, battery current and battery voltage along the top line. The bottom line will show distance in feet up to 65535 feet or in miles if the distance is greater than that, hours since last charged, and amp-hours since last charge.

When charge current is detected the display will switch to charge mode, where the top line will show “CHRG”, charging current, and battery voltage. The battery voltage field will alternate between peak voltage during charge and current voltage. The second line shows “CHRG”, total hours with charging current applied, and amp-hours of charge put into the battery since charging started.

The unit is calibrated like so: First, while connected to the charger and the charger indicating 15 amps, the ICAL button is pressed, which aligns the unit’s amperage measurement with the meter reading (15A) in the charger. To calibrate speed & distance, the SCAL pushbutton is pressed and held for 3 seconds (and the display will show “DRIVE 100 FT, PRESS SCAL”), the car is then driven exactly 100 feet and the SCAL pushbutton is pressed a second time.

For current measurements I will be measuring the voltage drop along the cable that connects the 1st battery to the second battery, and using this voltage and the calibrated 15A from the charger I’ll be able to calculate battery current with adequate accuracy. In testing I see around 10mV drop along this cable with 15A of charge current, in case you’re curious. For speed/distance measurements I’ll be tapping into the digital tach signal in the motor somewhere (haven’t yet dug into this very deeply but I know the signal is there somewhere - help here is welcome).

Think I’ve left anything out, or included useless stuff?

[E36Racer]

This seems interesting. Subscribed.

Where did you get the display? I’m surprised it is not using a shunt to measure pack amp draw from the main negative cable.


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[Wingsy]

Originally Posted by E36Racer

This seems interesting. Subscribed.

Where did you get the display? I’m surprised it is not using a shunt to measure pack amp draw from the main negative cable.

I am using a shunt. I'm using the resistance of the battery cable that connects the first 2 batteries as the shunt. The LCD doesn't come with a shunt, or anything else for that matter. It's just a generic LCD that I bought from Digikey.

This shunt's resistance can change primarily due to the contact resistance from the bolt/nut connection of the cable to the battery. It is why I am building in a calibration process to the device. It would need to be recalibrated every time the cable is removed and reconnected (rare instance, like when replacing the pack).

I think you're thinking that I'm putting this together from off-the-shelf systems. Not exactly. This is a design from scratch, really scratch (resistors, capacitors, chips, my own software). It's what I do, or did before I recently retired.

Do you know of an easy place to tap into the tech signal, or the characteristics of this signal?

[E36Racer]

I see. This project is WAY out of my wheelhouse then.

I don’t know if your motor has a bi-pole magnet or not. It should if it’s a sepex cart. Check for 3 wires in the motor end cap. Should be an 8 pole magnet if it’s stock.


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[Sergio]

The green wire on the speed sensor 3-pin connector is the output, 0-5v pulse.

There are 4 pulses per motor revolution as the sensor is bi-polar and the stock magnet has 8 poles (4 N/S pairs).

The differential has a 12.315:1 ratio (12.315 motor revolutions per wheel turn) for your speedometer math.

If You are using a 5v capable AVR type micro-controller, you can attach one of interrupt capable digital inputs directly to the Green wire.

Be careful with the Red wire on the 3-pin connector, it is 15v.

[Wingsy]

Originally Posted by Sergio

The green wire on the speed sensor 3-pin connector is the output, 0-5v pulse.

There are 4 pulses per motor revolution as the sensor is bi-polar and the stock magnet has 8 poles (4 N/S pairs).

The differential has a 12.315:1 ratio (12.315 motor revolutions per wheel turn) for your speedometer math.

If You are using a 5v capable AVR type micro-controller, you can attach one of interrupt capable digital inputs directly to the Green wire.

Be careful with the Red wire on the 3-pin connector, it is 15v.

Now THAT’S the kind of info I was looking for. Thank-you very much.

[jakesnake27]

This is gonna get good...

Way over my head though. Subscribed!

[Swan]

following along , i know enough to understand but not enough to build from scratch . this is going to be interesting for sure .

[LukeL]

Following along too


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[WalterM6]

I've got a suggestion. Can you make it readout in miles and tenths of miles only instead of feet. Is it large enough to be easily seen while driving?