Purpose

Design a function that converts 4 shock sensor ADC readings into usable shock travel values in millimeters for telemetry and suspension analysis.

The shock sensors are linear potentiometers whose signal sits close to 5 V when the shock is fully extended. When the suspension compresses, the voltage only decreases slightly.

The total useful signal range is approximately:

5.00 V → 4.86 V

So the actual change is only about 0.14 V.

Because the change is very small relative to the 5 V baseline, the code treats the difference from 5 V as the meaningful signal and scales that difference to the full mechanical travel of the shock.

Algorithm Overview

Initial Function

• Reset all stored shock sensor values
• Clear:
  • raw ADC readings
  • converted voltages
  • shock travel values in mm

This ensures startup begins with known values instead of stale sensor data.

Update Function

1. Read 4 ADC values

   • Inputs come in as rawReading1 through rawReading4

2. Invert ADC readings

   • Each reading is converted using:

abs(4095 - rawReading)

• The ADC is 12-bit, meaning values range from 0 to 4095.
• Because the sensor voltage decreases during compression, the raw ADC value behaves opposite of the desired interpretation of travel.
• Subtracting from 4095 flips the scale so that increasing compression produces increasing processed signal values.

3. Convert ADC counts to voltage

ADC_VALUE_TO_VOLTAGE(...)

This converts the processed ADC value into volts.

4. Use abs() on voltage

abs(ADC_VALUE_TO_VOLTAGE(...))

This ensures the voltage value is always non‑negative. It mainly acts as a safety guard against unexpected sign behavior.

5. Map voltage difference to shock travel

The shock signal only changes by 0.14 V across its usable range:

5.00 V → 4.86 V

The code maps that small change to the full suspension travel using:

(voltage / 0.14f) * SHOCK_TRAVEL_MAX_MM

Conceptually this means:

6. Clamp output

The computed travel is limited using:

constrain(value, 0.0f, SHOCK_TRAVEL_MAX_MM)

This prevents invalid sensor readings from producing impossible travel values.

Why abs() is used

1. Flipping the ADC scale

abs(4095 - rawReading)

The sensor begins near 5 V when fully extended, so the ADC reading starts close to the top of the ADC range.

As the shock compresses:

• Voltage drops slightly
• ADC value drops slightly

By subtracting from 4095, the scale is mirrored so the processed signal increases with compression.

The abs() ensures the result stays positive.

2. Protecting voltage conversion

abs(ADC_VALUE_TO_VOLTAGE(...))

This simply ensures the converted voltage value cannot become negative due to any intermediate math behavior.

The important calibration step is not abs() itself but recognizing that the signal range is only 0.14 V below 5 V.

Implementation Details

void Shock_Init()

Initializes all stored linear potentiometer data to zero.

Values cleared:

• raw ADC readings
• converted voltages
• shock travel values

This function runs once during startup.

void ShockTravelUpdateData(...)

Processes all four shock sensor ADC readings.

Steps:

1. Flip ADC readings using 4095 - rawReading
2. Convert processed ADC values to voltages
3. Interpret the small 0.14 V drop from 5 V as suspension compression
4. Scale that voltage change into millimeters
5. Clamp output values within the physical travel range

Linpot_GetData()

Returns a pointer to the shared linPots data structure.

Other modules can read:

• raw processed sensor values
• voltages
• shock travel in millimeters

This allows telemetry and future control algorithms to access suspension data.

Example

Example input

If the sensor is fully extended:

rawReading ≈ 4095

After inversion:

4095 - 4095 = 0

Voltage becomes near 5 V baseline, so travel ≈ 0 mm.

If the voltage drops by 0.07 V:

5.00 V → 4.93 V

That represents roughly half of the total 0.14 V span, so:

travel ≈ 0.5 × SHOCK_TRAVEL_MAX_MM

TESTING PLAN

Method Signature:

ShockTravelUpdateData(uint16_t rawReading1,
                      uint16_t rawReading2,
                      uint16_t rawReading3,
                      uint16_t rawReading4)

Constants:

ADC max count = 4095
voltage span = 0.14 V
minTravel = 0
maxTravel = SHOCK_TRAVEL_MAX_MM

TestCase 1 (Initialization)

Call:

Shock_Init()

Expected behavior:

• All voltages = 0
• All raw readings = 0
• All shock travel values = 0 mm

TestCase 2 (Fully Extended)

Inputs correspond to ~5 V:

rawReading ≈ 4095

Expected:

shockTravel = 0 mm

TestCase 3 (Mid Travel)

Voltage ≈ 4.93 V (half of 0.14 V span)

Expected:

shockTravel ≈ 0.5 × SHOCK_TRAVEL_MAX_MM

TestCase 4 (Full Compression)

Voltage ≈ 4.86 V

Expected:

shockTravel = SHOCK_TRAVEL_MAX_MM

TestCase 5 (Out of Range)

Voltage difference exceeds 0.14 V.

Expected:

constrain() clamps value to SHOCK_TRAVEL_MAX_MM