Signalling & test equipment
Turn-key design of a precision 56 kHz loop signal generator
A 24V DC-powered signal source with selectable Mark/Carrier/Space frequency outputs, switchable waveform type and independently adjustable output voltage.
Overview
What was delivered
XceedMinds delivered a turn-key engagement — spanning hardware, firmware and prototyping — for a precision 56 kHz loop signal generator powered from 24V DC.
The unit produces selectable Mark/Carrier/Space frequency outputs with switchable waveform type and independently adjustable output voltage, built around an STM32L431CBT6 MCU driving an AD9833 waveform generator IC.
- AD9833 DDS
- STM32L431
- ±0.01% accuracy
- < 5 ms switching
- PWM & analog gain
- 50Ω drive
The challenge
What made it difficult
The constraints that shaped every decision downstream.
Tight frequency precision at fast switching speed
Two waveforms, two output-voltage-control strategies
Driving a real load from a modest supply
Turn-key hardware, firmware and prototyping ownership
The solution
How it was built
Core design
An STM32L431CBT6 low-power MCU handles frequency selection, waveform switching and output voltage control logic, driving an AD9833 direct digital synthesis IC over SPI that generates both the square and sine waveforms with fine frequency resolution.
Firmware architecture
Peripheral and clock configuration were generated with STM32CubeMX and built out in STM32CubeIDE on the STM32Cube HAL/LL driver layers. SPI drives the AD9833’s frequency and phase registers, hardware timers generate the PWM duty-cycle output, and GPIO/EXTI interrupts handle the front-panel switches and LED indication.
Frequency control
A front-panel switch selects between the three Mark/Carrier/Space frequencies, each held to ±0.01% accuracy with switching latency under 5 ms — fast and precise enough for signalling applications sensitive to transition timing.
Output voltage control
Two independent control paths cover both waveforms: PWM mode adjusts the square wave’s duty cycle across a 25-45% range to shape output voltage, while analog mode adjusts gain directly for the sine wave output.
Output stage
Delivers ~35V RMS open circuit and ~400mA RMS into a 50Ω load, powered entirely from the 24V DC input rail.
Local operator interface
Dedicated switches for waveform type and frequency selection, each with LED indication, give the operator immediate, at-a-glance confirmation of the active configuration.
Specifications
Technical detail
The numbers the design had to hit.
- Power input
- 24V DC
- Output waveforms
- Square wave (default), sine wave
- Output voltage
- ~35V RMS, open circuit
- Output current
- ~400mA RMS into 50Ω load
- Square wave PWM
- Duty cycle adjustable 25-45%
- Frequency options
- Mark 55.6 kHz / Carrier 56.0 kHz / Space 56.4 kHz
- Frequency accuracy
- ±0.01%
- Switching latency
- < 5 ms
- MCU
- STM32L431CBT6
- Waveform generator IC
- AD9833 (SPI)
- Firmware toolchain
- STM32CubeMX, STM32CubeIDE, STM32Cube HAL/LL drivers, STM32CubeProgrammer (ST-Link/SWD)
Scope
Turn-key delivery
Everything carried under one engagement, with no handoff gaps between stages or vendors.
Hardware
Firmware
Prototyping
Highlights
What stands out
High-precision frequency synthesis
Fast, clean frequency switching
Dual waveform, dual output-voltage control
Turn-key delivery
Outcome
Where it ended up
A production-ready precision loop signal generator — spanning hardware, firmware and prototyping — unifying tightly-specified Mark/Carrier/Space frequency synthesis, dual-mode output voltage control and a robust 50Ω-load output stage into a single 24V DC-powered unit ready for evaluation and deployment.
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Building something similar?
Send a specification, a block diagram, or a description of the problem. We will come back with an honest view of scope, risk and the fastest route to a working prototype.