Very helpful thank you.
Chuck Walker
Here is what I have been able to put together with AI. I have purchased components spec’d by ChatGPT and Google Gemini is in agreement. I will follow with another email including the parts.
Chuck Walker
(Attachment Overview.docx is missing)
(Attachment Components.xlsx is missing)
(attachments)
Project summary.pdf (248 KB)
Arduino program.txt (4.69 KB)
That is fantastic, thank you. I tried to send you some documents but they got kicked back, evidently not allowed on the forum.
Chuck Walker
This is a word file I tried to send that got blocked I believe. All from ChatGPT, it really is amazing.
Great — here’s a vendor-ready BOM tailored for using the Arduino Nano with parts from DigiKey. I’ll list each key component with the DigiKey link (via product ID), quantity, and some notes.
Arduino Nano
$24.29
•
Mouser Electronics + others
IRLZ44NPBF MOSFET
$1.53
•
DigiKey + others
SMBJ15A TVS Diode
$0.24
•
DigiKey
SB540 Schottky Diode
$0.47
•
DigiKey
Bourns PDB241 Rotary Potentiometer
$3.91
•
DigiKey + others
TE Connectivity 282836‑6 6‑pin Terminal Block
$3.23
•
DigiKey + others
SB540‑T Schottky Diode (alternate)
$0.79
•
DigiKey
Bourns PDB241‑E420K Potentiometer Alternate
$2.46
•
DigiKey
Summary of each selection:
- Arduino Nano: Use for your MCU control/logic board. Workspace compatible and integrates well with your encoder and valve control.
- IRLZ44NPBF MOSFET: Logic-level power MOSFET rated ~55 V/47 A (datasheet shows drive at 4 V/10 V). Good margin for valve switching. DigiKey
- SMBJ15A TVS Diode: Automotive-grade transient suppression for your 12 V rail to protect board from load dumps. DigiKey+1
- SB540 Schottky Diode: Flyback diode across each valve coil to suppress back-EMF when MOSFET turns off.
- Bourns PDB241 Rotary Potentiometer: Panel-mount pot for remote mounting. You may need to select a variant with ~300-360° travel to match your knob sweep.
- TE Connectivity 282836‑6 6‑pin Terminal Block: Connector for remote valves harness (6-pin: +12 V, GND, 4 valve control lines).
- SB540‑T Schottky Diode (alternate): Alternate flyback diode listing for redundancy/spare part.
- Bourns PDB241‑E420K Potentiometer Alternate: Alternate version of panel pot if you want slightly different resistance or form-factor.
Here is the code Gemini created also.
// This Arduino sketch controls four 12V solenoid valves for an HVAC system
// based on the position of a rotary potentiometer using a CENTER-OFF control scheme.
// --- Pin Definitions ---
const int POT_PIN = A0; // Analog pin for the rotary control potentiometer
const int LEFT_VENT_PIN = 9; // Digital pin for Solenoid 1 (Left Vent)
const int RIGHT_VENT_PIN = 10; // Digital pin for Solenoid 2 (Right Vent)
const int DEFROST_PIN = 11; // Digital pin for Solenoid 3 (Defrost)
const int HEAT_VALVE_PIN = 3; // PWM pin for Solenoid 4 (Heat Modulation)
// Note: Ensure the MOSFET gate resistor and flyback diode are installed for each solenoid!
// --- Control Zone Definitions (Potentiometer reading 0-1023) ---
// The center-off position is assumed to be around 500-512.
// CCW side (0-500): Venting Modes
const int ZONE_BOTH_VENT_MAX = 150; // 7 o'clock (CCW Max)
const int ZONE_RIGHT_VENT_MAX = 300; // Between 7 and 9 o'clock
const int ZONE_LEFT_VENT_MAX = 450; // Close to 12 o'clock
// Center Dead Zone
const int ZONE_COLD_MIN = 451;
const int ZONE_COLD_MAX = 550; // 12 o'clock (Center/OFF)
// CW side (551-1023): Heating Modes
const int ZONE_HEAT_MAX = 850; // Transition from Heat to Defrost
const int ZONE_DEFROST_MIN = 851; // 4 o'clock to CW Max
void setup() {
// Initialize solenoid output pins
// Pins 9, 10, 11 will use digitalWrite (HIGH/LOW)
// Pin 3 (HEAT) will use analogWrite (PWM)
pinMode(LEFT_VENT_PIN, OUTPUT);
pinMode(RIGHT_VENT_PIN, OUTPUT);
pinMode(DEFROST_PIN, OUTPUT);
pinMode(HEAT_VALVE_PIN, OUTPUT);
// Start serial communication for debugging
Serial.begin(9600);
Serial.println("Bipolar HVAC Controller Initialized.");
// Ensure all valves start off
turnAllSolenoidsOff();
}
void loop() {
// Read the potentiometer value (0 to 1023)
int potValue = analogRead(POT_PIN);
// --- Map Solenoid State based on Potentiometer Zone ---
// *** COUNTER-CLOCKWISE ZONES (COLD/VENTING) ***
if (potValue <= ZONE_BOTH_VENT_MAX) {
// 1. BOTH VENT ZONE (Max CCW / 7 o'clock)
turnAllSolenoidsOff(); // Start fresh
digitalWrite(LEFT_VENT_PIN, HIGH);
digitalWrite(RIGHT_VENT_PIN, HIGH);
Serial.print("Zone: BOTH VENT (Pot Value: ");
Serial.print(potValue);
Serial.println(")");
} else if (potValue <= ZONE_RIGHT_VENT_MAX) {
// 2. RIGHT VENT ONLY ZONE (9 o'clock)
turnAllSolenoidsOff();
digitalWrite(RIGHT_VENT_PIN, HIGH);
Serial.print("Zone: RIGHT VENT (Pot Value: ");
Serial.print(potValue);
Serial.println(")");
} else if (potValue <= ZONE_LEFT_VENT_MAX) {
// 3. LEFT VENT ONLY ZONE (Closer to 12 o'clock)
turnAllSolenoidsOff();
digitalWrite(LEFT_VENT_PIN, HIGH);
Serial.print("Zone: LEFT VENT (Pot Value: ");
Serial.print(potValue);
Serial.println(")");
// *** CENTER DEAD ZONE ***
} else if (potValue >= ZONE_COLD_MIN && potValue <= ZONE_COLD_MAX) {
// 4. OFF / COLD ZONE (12 o'clock center position)
turnAllSolenoidsOff();
Serial.print("Zone: OFF / COLD (Pot Value: ");
Serial.print(potValue);
Serial.println(")");
// *** CLOCKWISE ZONES (HEATING/DEFROST) ***
} else if (potValue <= ZONE_HEAT_MAX) {
// 5. HEAT MODULATION ZONE (12 o'clock to 2 o'clock)
turnAllSolenoidsOff(true); // Turn off non-heat valves
// Map the potValue from the Heat Zone (551-850) to a PWM value (0-255).
// This allows smooth control from low heat (0) to high heat (255).
int pwmOutput = map(potValue, ZONE_COLD_MAX, ZONE_HEAT_MAX, 0, 255);
// Safety check: ensure the PWM value is non-negative
if (pwmOutput < 0) { pwmOutput = 0; }
analogWrite(HEAT_VALVE_PIN, pwmOutput);
Serial.print("Zone: HEAT Modulation (Pot Value: ");
Serial.print(potValue);
Serial.print(", PWM: ");
Serial.print(pwmOutput);
Serial.println(")");
} else { // potValue >= ZONE_DEFROST_MIN
// 6. DEFROST ZONE (2 o'clock to CW Max / 4 o'clock)
// For simplicity and safety, this zone is Defrost ON (High) with no heat modulation.
turnAllSolenoidsOff();
digitalWrite(DEFROST_PIN, HIGH);
Serial.print("Zone: DEFROST (Pot Value: ");
Serial.print(potValue);
Serial.println(")");
}
// Small delay to stabilize readings and prevent rapid switching
delay(50);
}
// Helper function to ensure all valves are closed
// The optional 'keepHeatPinLow' prevents accidentally setting HEAT_VALVE_PIN LOW
// using digitalWrite when we want to use analogWrite(0) elsewhere.
void turnAllSolenoidsOff(bool keepHeatPinLow = false) {
digitalWrite(LEFT_VENT_PIN, LOW);
digitalWrite(RIGHT_VENT_PIN, LOW);
digitalWrite(DEFROST_PIN, LOW);
// Setting PWM to 0 is the clean way to turn off a modulated solenoid
analogWrite(HEAT_VALVE_PIN, 0);
}
Chuck Walker
They were attached
You must use code tags <CODE/> when posting code, otherwise it does not come out right.
Just click on the icon and it will show
'''
type or post code here
'''
Also the BOM is a total mess
I suggest you buy the parts I recommended.
Jim, you have been a ton of help, thank you again.
Chuck Walker
The code did not compile it has an error wilh Allsolenoidsoff
Ok will use your part suggestion.
Hi, @wcw858
Have you checked that the valve solenoid you want to control with PWM, is suitable for PWM operation?
Tom.... 
Yes I have a rated valve for that.
Chuck Walker
Thank you please add it to my account.