How the buttons reach the ECU
When cruise is active, the Nexus uses the drive-by-wire throttle to hold the vehicle at the set speed. To know what the driver wants, it reads all of the cruise buttons through one analog input. Each button, when pressed, connects a different resistance between that input and signal ground. The ECU sees a different voltage for each one and works out which button is down.
That's the same resistor ladder trick most factory steering wheel controls use, so in many cars you can keep the OEM switches. In NSP the Input Type must be set to analog voltage.
Building your own button set
If you're making a switch panel from scratch, wire each button so that it puts its own resistor between the input and signal ground. Choose resistor values that spread the voltages out: each button's reading should be at least 0.1V away from every other one. More spacing is better, because wiring resistance, temperature and a bit of noise all move the reading slightly. We check each button live in NSP before calibrating the button voltages.
Which input to use
| Setting | AVI (preferred) | SPI (when no AVI is free) |
|---|---|---|
| Pull-up | 1k to 5V | Weak 10k to 5V |
| Sensor type | Not applicable | Set to Hall Effect for analog use |
| Pull-up on or off | On for a dedicated cruise switch. Off if the input is shared with another ECU (for example a piggyback beside the OEM ECU), because that ECU already supplies the pull-up. | |
Why does the pull-up matter? The resistor ladder only produces a voltage if something feeds current into it. The pull-up is that something. Two pull-ups on the same wire, one from each ECU, shift every button's voltage and can make buttons read as the wrong function.
The two pull-up strengths also give different voltage spreads with the same ladder, so if you move the switches from an AVI to an SPI, recheck and recalibrate the button voltages.
Indicator lights
Nexus cruise control can drive two lights. Each can be disabled, switched from a digital output (DPO) on the ECU, or switched over the vehicle CAN bus.
- Enable light: on whenever the Cruise Control State is anything other than Disabled. Think of it as "cruise is armed."
- Active light: on when the state is Cruising, Accelerating or Coasting, meaning the ECU is actually holding or changing speed.
For a hard-wired light, choose a spare DPO or stepper output. Most dash lamps and LEDs get 12V from the ignition feed and are switched on by the ECU grounding the other side.
Active State
| Active State | Light should be on | Light should be off |
|---|---|---|
| Low (default) | Output grounded | Output not grounded |
| High | Output not grounded | Output grounded |
Low suits nearly every lamp wired as above. Use High only when the device on the other end expects the inverted logic.
Troubleshooting
| Symptom | Usually |
|---|---|
| Wrong function when a button is pressed | Button voltages too close together, or two pull-ups on a shared wire |
| Input sits at 0V or never changes | Pull-up disabled on a dedicated switch, or the ground side isn't connected |
| Readings jumped after changing input | Moved between AVI and SPI; different pull-ups need recalibrating |
| Light works backward | Active State set to High on a ground-switched lamp |
Where to go next
Once the wiring reads cleanly, assign the functions in cruise control buttons, then tune the speed controller with the proportional, integral and derivative gains. The function overview is in cruise control.
Can I use my factory steering wheel buttons?
Usually, if they're a single-wire resistor ladder. Measure each button's voltage in NSP and confirm they're well separated.
Do I need drive-by-wire?
Yes. The Nexus holds speed by controlling the electronic throttle, so a cable throttle won't work with this function.
