DPS-150 Power Supply Controller

A Python desktop application for controlling up to three FNIRSI DPS-150 programmable power supplies simultaneously over USB serial, with integrated closed-loop magnetic field compensation via a WitMotion HWT3100-485 fluxgate magnetometer.

Python/PySerial port of the fnirsi-dps-150 WebSerial interface.

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Features

• Three simultaneous devices — connect and control three DPS-150 units independently from one window
• Live meters — real-time voltage, current, and power readings at 500 ms refresh
• CV / CC mode indicator and protection fault badges (OVP / OCP / OPP / OTP / LVP)
• Setpoint controls — entry fields with ▲ / ▼ steppers and Enter-to-apply for V and I
• Always-visible history plots — voltage and current traces for all three devices side by side
• Magnetometer PID compensation — closed-loop Helmholtz coil driver using the HWT3100-485 and the three DPS-150 units as X / Y / Z axis coil drivers
• Per-device tabs for Metering (Ah / Wh), Protections (OVP/OCP/OPP/OTP/LVP), Program (DSL scripting), and Settings (brightness / volume)
• DSL scripting — automate sequences with V(), I(), ON(), OFF(), SLEEP(), times()
• CSV export of measurement history

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Hardware

Device	Interface	Notes
FNIRSI DPS-150 (×3)	USB serial, 115200 baud	One per Helmholtz coil axis
WitMotion HWT3100-485	Modbus RTU / RS-485	Via USB-to-RS485 adapter (CH340 or CP2102)

Wire each Helmholtz coil pair so that positive current on its DPS-150 output opposes the ambient field on that axis (Dev 1 → X, Dev 2 → Y, Dev 3 → Z).

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Installation

pip install pyserial customtkinter matplotlib

Run:

python main.py

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Usage

Power supply control

1. Click ⟳ Scan ports to populate the port dropdowns
2. Select the correct COM port for each device and click Connect
3. Type a voltage or current setpoint and press Set V / Set I (or Enter)
4. Toggle OUTPUT ON / OFF per device

Magnetometer & PID compensation

1. Open the Magnetometer tab
2. Select the magnetometer's COM port, set baud rate (default 9600) and Modbus address (default 0x00), then click Connect
3. Configure per-axis calibration:
   • A / μT — coil calibration constant. For a Helmholtz pair with radius R and N turns per coil: I/B = R / ((4/5)^(3/2) × μ₀ × N). Example: N = 100, R = 0.15 m → ~0.00084 A/μT
   • Polarity — set to -1.0 if your coil winding opposes the convention
   • Max V / Max I — compliance voltage and current clamp per axis
4. Set PID gains (Kp, Ki, Kd), integral limit, and loop interval
5. Set field target (default 0, 0, 0 μT)
6. Click ▶ Start PID — the loop runs, adjusting DPS-150 current setpoints to zero the field
7. Click ■ Stop to ramp currents to zero and disable outputs

DSL scripting

Write programs in the Program tab using the built-in DSL:

# Ramp voltage from 1 V to 5 V in 0.2 V steps
V(1)
I(0.5)
ON()
SLEEP(500)
while V() + 0.2 <= 5:
    V(V() + 0.2)
    SLEEP(200)
OFF()

Available functions:

Function	Description
V(v)	Set voltage to v V (or read current output voltage if no arg)
I(a)	Set current limit to a A (or read current output current if no arg)
ON()	Enable output
OFF()	Disable output
SLEEP(ms)	Wait ms milliseconds
times(n, fn)	Repeat fn n times

The Tab target selector above the tabs determines which device the Program, Metering, Protections, and Settings tabs operate on.

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Serial Protocol

The DPS-150 uses a binary framing protocol at 115200 baud 8N1:

TX (host → device):  F1 <CMD> <PARAM_ID> <LEN> <PAYLOAD> <CHECKSUM>
RX (device → host):  F0 <CMD> <PARAM_ID> <LEN> <PAYLOAD> <CHECKSUM>

Checksum = (PARAM_ID + LEN + Σ PAYLOAD) mod 256. Payload floats are little-endian IEEE-754 32-bit. Register 0xFF returns all device state in one bulk frame.

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Project Structure

File	Purpose
main.py	Full application — DPS-150 driver, PID controller, UI
magnetometer.py	WitMotion HWT3100-485 Modbus RTU driver
requirements.txt	Python dependencies

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Credits

• Serial protocol reverse-engineered from cho45/fnirsi-dps-150
• Magnetometer PID compensation architecture adapted from compensation-magnetometer-controls