This STM32-based instrument has the following features:
- Output signal with synchronized auxiliary output for re-triggering.
- Input signal trigger using frequency or voltage.
- User-modifiable output attributes including function, frequency, gain and DC offset.
- Frequency Sweep mode.
- RGB colour TFT LCD display.
- Small form factor.
| Attribute | Limits |
|---|---|
| Power Supply | 9 Volts 163 mA DC Center-positive 2.1mm barrel jack Reverse-polarity protected |
| Input/Output connectors | BNC 400W TVS protection |
| Function | Sine Square Ramp Reverse Ramp Triangle Pulse PWM (aux output only) |
| Frequency | 0.1Hz - 100KHz |
| Gain | 40 dbmV - 79.8 dbmV 0.1 Vpp - 9 Vpp |
| DC offset | +/- 9V |
| Output Noise (100KHz) | -76 db (10KΩ) -60 db (500Ω) 11 nV/√Hz |
| Output Current | 10 mA nominal 20 mA peak |
| Sweep | 12.5 sec per step (max) 0.59 nanosec per step (min) |
| Input trigger range | See "Voltage Measurements" section |
| Dimensions | Height: 70mm Width: 170mm Depth: 170mm |
Project details for the hardware can be found here
Full STM32Cube report be found here.
List of timer peripherals and their system functions:
| Timer | Function | Notes |
|---|---|---|
| TIM1 | Rotary Encoder | Encoder Mode TI2 |
| TIM2 | Input Trigger | Input Capture Direct Mode (see Input Trigger section). Preload Enabled |
| TIM3 | PWM function | AUX output only |
| TIM5 | Frequency Sweep | Both outputs (32bit timer) |
| TIM8 | DAC Trigger | Update Event. Preload Enabled |
| TIM15 | Display Manager | Calls DM_UpdateDisplay() |
| TIM16 | Button debounce | |
| TIM17 | Event Manager | Called EM_ProcessEvent() |
This project contains a modified and optimized ILI9341 Library: Optimized_STM32_ILI9341
- Optimized to use direct-to-register SPI for single- and multi-byte transfers (MOSI only). This offers a noticeable performance boost over HAL API.
- Draw functions were modified to use x,y,width,height parameters.
- Additional draw functions from STMBasicGUI were included.
The original version of the STM32-ILI9341 library.
EventManager.h defines system states and events for the menu display and user controls (buttons and rotary encoder).
| eSystemState |
|---|
| Toplevel_Main_Menu_State |
| Toplevel_Output_Menu_State |
| Toplevel_Input_Menu_State |
| Func_Main_Menu_State |
| Func_Signal_Menu_State |
| Func_Aux_Menu_State |
| Gain_Main_Menu_State |
| Gain_Signal_Menu_State |
| Gain_Aux_Menu_State |
| Freq_Main_Menu_State |
| Freq_Preset_Menu_State |
| Freq_Adjust_Menu_State |
| Freq_Sweep_Menu_State |
| Freq_Prescaler_Menu_State |
| Bias_Menu_State |
| Idle_State = Toplevel_Main_Menu_State |
| eSystemEvent |
|---|
| evIdle, |
| evBlueBtn, |
| evGreenBtn, |
| evYellowBtn, |
| evRedBtn, |
| evEncoderSet, |
| evEncoderPush, |
| evSweepEnableBtn, |
| evSweepModeBtn, |
| evSweepSpeedBtn, |
| evSweepLimitBtn, |
Active event and state are held in global variables eNextState and eNewEvent, respectively.
Interrupts triggered by the buttons and rotary encoder are processed by InterruptManager.c, which sets the global event variable to the appropriate event.
The EM_ProcessEvent function is periodically called by Timer #17.
EM_ProcessEvent selects the current state and calls the related event handler for the new event. A simplified version is shown below:
void EM_ProcessEvent()
{
switch(eNextState)
{
case someState1:
if(eNewEvent == evSomeEvent1)
eNextState = doSomeEventHandler1();
break;
if(eNewEvent == evSomeEventN)
eNextState = doSomeEventHandlerN();
break;
case someStateN:
....
}
}
The Event handler for the new event is called and returns the next system state.
Business logic for Top level menu, Function menu, Frequency menu, Gain menu and Offset Bias menu are delegated to separate files.
DisplayManager.h defines a standard colour palette used by the graphics library.
The ILI9341 LCD driver IC has a very low refresh rate. To avoid flicker, the background is redrawn only on eSystemState change (when the user navigates to a different menu screen). All text is periodically redrawn by Timer15, which executes DM_UpdateDisplay() function. To avoid flicker, text strings must be positioned so that they do not overlap.
The DisplayManager queries the active system state and determines which menu is to be enabled. The business logic of drawing the menus is delegated to seperate files. The system state variable is passed to the file for further sub-menu delegation.
The output function of the device is generated through a series of wavetables. These wavetables are generated using python scripts into C source files. The python scripts and wavetable source files can be found in the WaveTableGeneration directory.
The wavetables are generated at 120 samples per second and offset above the zero point. The wavetable data is loaded into DAC1 Channel 1 via DMA, which is triggered via Timer 8. This timer must have its auto-reload preload enabled so that the DMA peripheral is not interruped mid-cycle. Interrupting the DMA peripherla mid-cycle can cause the DAC output to randomly fail.
DC voltage is output from DAC1 Channel 2. This offset is (optionally) inverted and mixed with the output signal from DAC1 Channel 1 to provide DC offset at the device output.
A PGA was included in the HW design to provide gain at the device output. However, the settling time of the PGA was insufficient, which caused significant "jitter". Therefore, the PGA is left at maximum gain, whilst realtime gain adjustments are achieved in SW by modifying the amplitude of the wavetable data.
An auxiliary output is also provided on pin PA6 using DAC2 Channel1. This aux output uses the same trigger timer (TIM8) as DAC1 and so is syncronized with the main output signal. The auxiliary output provides same signal functions plus a pulse width modulated function. This is achieved by disabling the DAC2 Channel1 output and redirecting the Output Compare register of TIM3 on pin PA6.
The output frequency of all outputs are adjusted simulataneously by modifying the reload register of the trigger timer (TIM8).
A frequency sweep feature is also implemented.
Input trigger function including external multiplexing, DMA callbacks, frequency and voltage measurements are handled by InputTrigger.c
An external "TS5A3357" SP3T switch (datasheet) selects the input signal path into the microcontroller.
| IN1 | IN2 | FUNCTION |
|---|---|---|
| H | L | TIM2 (PA0) |
| L | H | COMP (PA1) |
| H | H | ADC (PA2) |
TS5A3357 pins IN1 and IN2 are set/reset by microcontroller pins PC8 and PC9, respectively.
In "Time Mode" the input signal frequency is measured using reciprocal counting methods with TIM2.
- When this mode is enabled TIM2 is enabled and begins counting to 0xFFFF.
- The input signal is externally multiplexed into port PA0 (set to alt. function TIM2_CH1).
- This is internally multiplexed using the interconnect to "tim_ti1_in0".
- A rising edge detected on the input signal triggers a "tim_ti1_fp1" signal to Input Capture Channel 1 and the slave controller.
- TIM2 is configured to reset its count on "tim_ti1_fp1" trigger signal. This sends an write request to the DMA controller and contents of CCR1 is written to memory.
-
On timer capture callback, the frequency in hertz is then calculated:
Freq = MCLK / (TIM2->PSC * TIM2->CCR1) -
Longer processing delays for input frequencies lower than 50Hz are expected.
-
At these lower frequencies the input trigger automatically enters "LF Mode" and adjusts the prescaler to improve resolution/accuracy.
The ADC measures the voltage level of the input signal and compares it - within the nearest 0.05V - to the values in the following lookup table:
| note | volts | hertz | period |
|---|---|---|---|
| C0 | 0.08 | 16.35 | 42813 |
| C#0 | 0.17 | 17.32 | 40416 |
| D0 | 0.25 | 18.35 | 38147 |
| D#0 | 0.33 | 19.45 | 35990 |
| E0 | 0.42 | 20.60 | 33981 |
| F0 | 0.50 | 21.83 | 32066 |
| F#0 | 0.58 | 23.12 | 30277 |
| G0 | 0.67 | 24.50 | 28571 |
| G#0 | 0.75 | 25.96 | 26965 |
| A0 | 0.83 | 27.50 | 25455 |
| A#0 | 0.92 | 29.14 | 24022 |
| B0 | 1.00 | 30.87 | 22676 |
| C1 | 1.08 | 32.70 | 21407 |
| C#1 | 1.17 | 34.65 | 20202 |
| D1 | 1.25 | 36.71 | 19068 |
| D#1 | 1.33 | 38.89 | 17999 |
| E1 | 1.42 | 41.20 | 16990 |
| F1 | 1.50 | 43.65 | 16037 |
| F#1 | 1.58 | 46.25 | 15135 |
| G1 | 1.67 | 49.00 | 14286 |
| G#1 | 1.75 | 51.91 | 13485 |
| A1 | 1.83 | 55.00 | 12727 |
| A#1 | 1.92 | 58.27 | 12013 |
| B1 | 2.00 | 61.74 | 11338 |
| C2 | 2.08 | 65.41 | 10702 |
| C#2 | 2.17 | 69.30 | 10101 |
| D2 | 2.25 | 73.42 | 9534 |
| D#2 | 2.33 | 77.78 | 9000 |
| E2 | 2.42 | 82.41 | 8494 |
| F2 | 2.50 | 87.31 | 8017 |
| F#2 | 2.58 | 92.50 | 7568 |
| G2 | 2.67 | 98.00 | 7143 |
| G#2 | 2.75 | 103.83 | 6742 |
| A2 | 2.83 | 110.00 | 6364 |
| A#2 | 2.92 | 116.54 | 6007 |
| B2 | 3.00 | 123.47 | 5669 |
| C3 | 3.08 | 130.81 | 5351 |
| C#3 | 3.17 | 138.59 | 5051 |
| D3 | 3.25 | 146.83 | 4767 |
| D#3 | 3.33 | 155.56 | 4500 |