Why use a switch to log?
Elite ECUs can record to their own internal memory, no laptop required. A physical switch gives the driver direct control: flick it on before the run you care about, flick it off after. That keeps logs short and easy to find, which matters when you're sending them to us for review.
Two things have to be set up. First, the switch input itself, covered below. Second, in Main Setup, Datalog, Activation Condition, you have to choose the datalogging switch as the thing that starts and stops logging. Skip that second step and the switch will read perfectly in ESP but never start a log. Our Elite datalog article covers the rest of the logging settings.
Choosing an input
Either an SPI (synchronized pulsed input) or an AVI (analog voltage input) will work. Which one you use mostly comes down to what you have spare. They're configured differently, though.
| SPI | AVI | |
|---|---|---|
| How it decides on/off | Watches for a signal edge | Compares the voltage with two thresholds you set |
| Settings | Edge Select, Sensor Type, Pullup | Switch On Voltage, Switch Off Voltage |
| Good for | A simple switch to ground or to 12V | Odd voltage levels, or when SPIs are all used |
SPI settings
- Edge Select: choose Falling if the switch connects the input to ground when you turn it on. Choose Rising if the switch feeds voltage to the input when it's on.
- Sensor Type: always Hall Effect for a switch.
- Pullup: turn it on when the input needs something to hold it high while the switch is off. A switch to ground almost always needs it, otherwise the wire just floats.
AVI settings
With an AVI, you give the ECU two voltages: one that means on and one that means off. The gap between them is deliberate. It's hysteresis, and it stops the input chattering if the voltage wanders a little because of charging system noise or a tired switch.
Work out your two thresholds like this:
- Measure (or look up) the voltage the input sees with the switch off, and with it on.
- Set the Switch On Voltage a little inside the on level, toward the off side.
- Set the Switch Off Voltage a little inside the off level, toward the on side.
- Leave a clear gap between the two.
Worked example: switch to ground
Say the input is pulled up and sits near 5V with the switch off, then drops to about 0V when you flip the switch. Setting On at 1.0V and Off at 4.0V means the ECU calls it on once the voltage falls under 1.0V, and only calls it off again after it climbs back past 4.0V. A tighter pair, such as 0.5V and 4.5V, also works with a clean switch.
Worked example: switch to 12V
Now the reverse: the input idles at a middle voltage, around 2.5V, and sees battery voltage when switched on. Here On goes above the resting level and Off goes just over it. On at 4.5V and Off at 3.0V gives you a switch that turns on as the voltage rises past 4.5V and turns off once it sinks back below 3.0V.
Before feeding battery voltage to any ECU input, confirm in your ECU's pinout that the input you've chosen is rated for it.
Hardware
Any latching switch works, but a tidy option is a Haltech dual switch panel kit or triple switch panel kit, which leaves room for other functions like launch control or a map switch.
Troubleshooting
| Symptom | Usually |
|---|---|
| Switch reads fine, but no logs appear | Activation Condition in Main Setup, Datalog isn't set to the switch |
| SPI never changes state | Wrong edge, or no pullup on a switch-to-ground circuit |
| Logging starts and stops by itself | AVI thresholds too close together, or a poor switch ground |
| AVI stuck on or off | On and Off voltages entered the wrong way around for your circuit |
On a Nexus ECU? The NSP equivalent is covered in our Nexus datalog switch article.
