sensorstm32ultrasound
I've connected the sensor this way, from Sensor to Board:
VCC -> 5V
GND -> GND
Trigger -> PD15 ( same as blue led )
Echo -> PA0 ( same as user button )
My C program send the trigger, reads the input and calculates the distance in cm.
However as I lack basic electronics knowledge, I'm worried this setup might damage the board or sensor.
Do I have to add any resistor or diode or anything to protect the components?
The problem with hobby related solutions is documentation is limited and not spec'd like commercial components or modules.
It is possible that it may work but make a block wiring diagram and consult with the OEM is advised. Mind you I don't know if they have adequate support for your question as these are built in China.
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It appears that your ultrasonic load is TTL so there is no problem switching 5 at the same time with a BEC, but I wonder if you have considered the effects of crosstalk on firing all at the same time. They indicate a 15deg detection angle but this would depend on the reflection angle of objects you wish to detect. There may be phasing issues with reflection cancellations like having 5 tweeters directed in a room. Reading the response of each echo in parallel with a time interval count won't be a simple textbook result with non-smooth objects with 5 senders.
YOu can test your orthogonal array design with any signal pulse generator and look at the signal on a parallel port logic analyzer or scope to ensure what you are design will work.
Power drive is the least of your concerns from these low power devices. Noise avoidance from conducted and radiated sources will be paramount and design of the transponder array must come first. I would spend some time on testing this part 1st to identify all the electrical, physical, acoustic, EMI, thermal, vibration both conducted and radiated sources of interference and how each affects your SONAR expectations with different objects. Will it be microphonic with vibration or loud pulse noises. How well does it reject other ultrasound sources of noise? Will the TTL Echo output change in pulse width with signal strength or just the delay time.
Will you get echos from the wrong sender due to corner refection effects.
When working with the STM32F4-Discovery board (or any similar board), you have to make sure that the pins of the microcontroller you want to use are not already in use by another component on the board. The user manual for the STM32F4-Discovery has table 5, which shows you exactly which IO pins are in use, and which are free. If they are not free, you may still be able to use them, but you will need to check on the schematic how exactly they are connected to other components, and how those components might affect the desired operation. In your case, pins PA9 and PA10 are not free (they are connected to the USB port and a LED), which most likely interferes with the serial communication.
Best Answer
I'm going to start by saying I couldn't find a good data sheet for that Sensor.
The best information I found is Arduino Ultrasonic Ranging
AFAICT, the Sensor needs a 5V signal on its 'Trig' trigger input. So the bad news is the electronics will need to be a tiny bit more complex.
The STM32F4 can not drive a 5V signal directly. The highest voltage its pins can drive is a bit (0.4V) less than its power supply, which is 3.3V.
But, the STM32F4 has plenty of pins which are called '5 Volt Tolerant (FT)'. These pins can't drive 5V directly, but they can be connected to something at 5V without damage (1). You will need to look at ST Micro's STM32F407 datasheet to choose 5V tolerant pins.
So FT pins can connect a signal to ground, i.e. pull the signal low, but not drive it high. This is where a good datasheet would be very helpful. The sensors trigger input wants to be at 5V, but it doesn't say if it needs much current. I will assume it doesn't need much. So I will assume a resistor could be connected between the trigger pin and 5V. That resistor would pull-up the trigger pin, and cause the sensor to trigger. I would guess a 1Kohm resistor would be fine.
So connect a 5V Tolerant output of the STM32F4 to the trigger pin/resistor. The STM32F4 will pull the pin low to disable the sensor, and let it get pulled high by the resistor to enable the sensor (by setting the pin high).
Your software must configure the STM32F4 output pin to be 'Open Drain'. Normally, the software will set the pin low, which will keep the trigger off. Then when the programs wants to trigger the sensor, set the pin high for more than 10useconds, and the sensor should start broadcasting. (As long as the pin has been put into Open Drain output mode, it should work). You can check the trigger signal is working by (bfore connecting the sensor) with a voltmeter.
The other part of the system is connecting the Echo output from the sensor to an input on the STM32F4. That also looks like a 5V signal. I think that a 5V Tolerant pin on the STM32F4 will be okay upto 5.5V. To start with, I'd take make a voltage divider with a couple of resistors in series. Connect the sensors Echo pin to one end of the resistor pair, and the other end to ground. Connect the 'middle' to the STM32F4 input pin. It should work with a couple of 1K resistors, but three in series with two between the STM32F4 input and ground would be even better.
So, for the cost of a few resistors. You should be okay.
Further Suggestions: If you have access to an oscilloscope, you should be able to see the Echo signal, and check on its voltage.
If the Trigger signal is not enough current to drive the sensor, then it'll need a bipolar transistor or MOSFET to pull the signal high. Cost less than $1, so not a big problem). I would be surprised if this were a problem, but it might be.
1) Note: connecting an STM32F4 pin, which is not 5v Tolerant to 5V may irreparably damage that pin, and maybe worse)