Libraries & Hardware

Stm32f103C8 External Dac

stm32user
Mon Jan 15, 2018 12:54 pm
Hello there

I want to use an external DAC in Stm32f103c8.

How can I get a value of 0-255 as 8 logic output.

thax :roll:

Pito
Mon Jan 15, 2018 1:02 pm
Which external DAC, give us the link..
stm32user
Mon Jan 15, 2018 1:11 pm
[Pito – Mon Jan 15, 2018 1:02 pm] –
Which external DAC, give us the link..

I do not have any schematics.

For example PA0 PA1 PA2 PA3 PA4 PA5 PA6 I can get 8 outputs with for 0-255 data.

or if the outputs are different

PA0, PA1, PB2, PB5 etc.

Pito
Mon Jan 15, 2018 1:52 pm
With 103C8 you may use

analogWrite(pin, value); // value 0 - 255

analogWrite(PA7, 189);

or

pwmWrite(pin value); // value 0 - 65535

dannyf
Mon Jan 15, 2018 1:58 pm

How can I get a value of 0-255 as 8 logic output.

generally you write a piece of code, as per the datasheet of your external DAC, to communicate with it.

that works 100% of the time with 100% of the devices, DAC or not.

Pito
Mon Jan 15, 2018 2:06 pm
Be more specific, what external DAC you want to use (if any)?
There are R2R DACs, 1-2-4-8..R DACs, I2C DACs, SPI DACs, parallel DACs, PWM DACs, etc..
stm32user
Mon Jan 15, 2018 2:14 pm
Image

can we do it like the picture?

Pito
Mon Jan 15, 2018 2:16 pm
That is the R2R DAC.
Yes you can do it, sure. You may wire it to a port, ie. PortA or PortB, PA0-PA7 or PB0-PB7, and then send the DAC value to the PortA or PortB in a single write.
Mind the stm32 is a 3.3Volt device, thus the R2R output will be 0..3.28V max.
stm32user
Mon Jan 15, 2018 2:34 pm
Thanks for the answer, if I want to use different pins?

PA0, PA1, PA2, PB12, PB13, PB14, PA3, etc.

There is a method

Pito
Mon Jan 15, 2018 2:48 pm
You may set the bits individually. First set the individual pins to outputs, then write the DACvalue:

pinMode(PA0, OUTPUT);
..
pinMode(PB12, OUTPUT);
..
// write the DACvalue 0-255, 8bit
digitalWrite(PA4, (DACvalue & 0x80)); // the highest DACvalue bit7
digitalWrite(PA3, (DACvalue & 0x40));
digitalWrite(PB14, (DACvalue & 0x20));
digitalWrite(PB13, (DACvalue & 0x10));
digitalWrite(PB12, (DACvalue & 0x08));
digitalWrite(PA2, (DACvalue & 0x04));
digitalWrite(PA1, (DACvalue & 0x02));
digitalWrite(PA0, (DACvalue & 0x01)); // the lowest DACvalue bit0
..

Vassilis
Mon Jan 15, 2018 3:49 pm
The R2R DAC requires an Operational Amplifier (OP_AMP) to get some mΑ to the output. For example, you can not drive an LED with the R2R dac as-is. You need to use an OP-AMP such as LMV358.

If I were you, I would use an SPI DAC such as MCP4921 (single DAC) or MCP4922 (double DAC) that can provide 25mA output as-is ;)

dannyf
Mon Jan 15, 2018 5:18 pm
You may set the bits individually.

Just think about the values the DAC outputs while those pins are being set / reset.

you will need a mechanism to latch the output.

Pito
Mon Jan 15, 2018 6:00 pm
He may apply an algorithm, where the bits between the DAC samples change such the turmoil at the output will be minimal :)
stevestrong
Mon Jan 15, 2018 6:39 pm
What is the final goal?
Can’t be solved by using a filtered PWM output?
dannyf
Mon Jan 15, 2018 11:18 pm
He may apply an algorithm

I don’t know how that can be addressed via software. a latch, including a latch-equipped shift register, would be my way to go for glitch-free output. Otherwise, a capacitor can help reduce the glitches, with performance issues of its own however.

stm32user
Tue Jan 16, 2018 3:09 pm
uint8_t DPINS[] = {PA0, PB0, PA1, PB0, PB12, PB13, PB14, PB15}; // random pin

void setup(){

for (uint8_t i = 0; i <= sizeof(DPINS) - 1; i++)
pinMode(DPINS[i], OUTPUT);
}

num = sine[i]; // sine table value

for (byte i=0; i<= sizeof(DPINS) - 1; i++) {
byte state = bitRead(num, i);
digitalWrite(DPINS[i], state);
}

Vassilis
Tue Jan 16, 2018 5:33 pm
try that code


uint8_t DPINS[] = {PA0, PB0, PA1, PB1, PB12, PB13, PB14, PB15}; // random pin
uint8_t num;

uint8_t sine[256] = {
0x80, 0x83, 0x86, 0x89, 0x8C, 0x90, 0x93, 0x96,
0x99, 0x9C, 0x9F, 0xA2, 0xA5, 0xA8, 0xAB, 0xAE,
0xB1, 0xB3, 0xB6, 0xB9, 0xBC, 0xBF, 0xC1, 0xC4,
0xC7, 0xC9, 0xCC, 0xCE, 0xD1, 0xD3, 0xD5, 0xD8,
0xDA, 0xDC, 0xDE, 0xE0, 0xE2, 0xE4, 0xE6, 0xE8,
0xEA, 0xEB, 0xED, 0xEF, 0xF0, 0xF1, 0xF3, 0xF4,
0xF5, 0xF6, 0xF8, 0xF9, 0xFA, 0xFA, 0xFB, 0xFC,
0xFD, 0xFD, 0xFE, 0xFE, 0xFE, 0xFF, 0xFF, 0xFF,
0xFF, 0xFF, 0xFF, 0xFF, 0xFE, 0xFE, 0xFE, 0xFD,
0xFD, 0xFC, 0xFB, 0xFA, 0xFA, 0xF9, 0xF8, 0xF6,
0xF5, 0xF4, 0xF3, 0xF1, 0xF0, 0xEF, 0xED, 0xEB,
0xEA, 0xE8, 0xE6, 0xE4, 0xE2, 0xE0, 0xDE, 0xDC,
0xDA, 0xD8, 0xD5, 0xD3, 0xD1, 0xCE, 0xCC, 0xC9,
0xC7, 0xC4, 0xC1, 0xBF, 0xBC, 0xB9, 0xB6, 0xB3,
0xB1, 0xAE, 0xAB, 0xA8, 0xA5, 0xA2, 0x9F, 0x9C,
0x99, 0x96, 0x93, 0x90, 0x8C, 0x89, 0x86, 0x83,
0x80, 0x7D, 0x7A, 0x77, 0x74, 0x70, 0x6D, 0x6A,
0x67, 0x64, 0x61, 0x5E, 0x5B, 0x58, 0x55, 0x52,
0x4F, 0x4D, 0x4A, 0x47, 0x44, 0x41, 0x3F, 0x3C,
0x39, 0x37, 0x34, 0x32, 0x2F, 0x2D, 0x2B, 0x28,
0x26, 0x24, 0x22, 0x20, 0x1E, 0x1C, 0x1A, 0x18,
0x16, 0x15, 0x13, 0x11, 0x10, 0x0F, 0x0D, 0x0C,
0x0B, 0x0A, 0x08, 0x07, 0x06, 0x06, 0x05, 0x04,
0x03, 0x03, 0x02, 0x02, 0x02, 0x01, 0x01, 0x01,
0x01, 0x01, 0x01, 0x01, 0x02, 0x02, 0x02, 0x03,
0x03, 0x04, 0x05, 0x06, 0x06, 0x07, 0x08, 0x0A,
0x0B, 0x0C, 0x0D, 0x0F, 0x10, 0x11, 0x13, 0x15,
0x16, 0x18, 0x1A, 0x1C, 0x1E, 0x20, 0x22, 0x24,
0x26, 0x28, 0x2B, 0x2D, 0x2F, 0x32, 0x34, 0x37,
0x39, 0x3C, 0x3F, 0x41, 0x44, 0x47, 0x4A, 0x4D,
0x4F, 0x52, 0x55, 0x58, 0x5B, 0x5E, 0x61, 0x64,
0x67, 0x6A, 0x6D, 0x70, 0x74, 0x77, 0x7A, 0x7D
};

void setup(){
for (uint8_t i = 0; i <= sizeof(DPINS) - 1; i++)
pinMode(DPINS[i], OUTPUT);
}

void loop() {
for(int m=0;m<255;m++){
num = sine[m]; // sine table value
for (byte i=0; i <= sizeof(DPINS)-1; i++) {
byte state = bitRead(num, i);
digitalWrite(DPINS[i], state);
}
}
}

Pito
Tue Jan 16, 2018 10:47 pm
Try to order the changing the DACvalue bits from the highest bit to the lowest (as I did in my code above).
Like in your code:
for (byte i=7; i >=0; i--) {
byte state = bitRead(num, i);
digitalWrite(DPINS[i], state);
}
dannyf
Wed Jan 17, 2018 1:50 pm
If you want speed, don’t use digitalWrite, unroll the loop and use a pointer to index the array.
Pito
Wed Jan 17, 2018 2:19 pm
The fastest way would be to generate a set of DAC “commands” like
..
sample_delay();
// *********************** Output the Sample N. 345 ************************
//Set A2, A12, A13 (HIGH)
GPIOA->regs->BSRR = 0b0011000000000100;
//Clear A3, A11, A15 (LOW)
GPIOA->regs->BRR = 0b1000100000001000;
//Set B1, B12, B15 (HIGH)
GPIOB->regs->BSRR = 0b1001000000000010;
//Clear B3, B11, B13 (LOW)
GPIOB->regs->BRR = 0b0010100000001000;
// *************************************************************************
sample_delay();
..
racemaniac
Wed Jan 17, 2018 2:20 pm
Reminds me of my first lightsaber iteration, i went for a similar setup to what OP is trying here. But i did choose consecutive pins (for example PA0 -> PA7), so i could do a write directly to the port registers with my binary data, making it very fast :).
Rather than actually building my own R2R ladder, i used an IC that basically consists of such a ladder, and then 2 amps behind it to get sound from it all :).
Pito
Wed Jan 17, 2018 2:39 pm
You may write an R2R DAC sample in 4 clocks (~56ns) with any pins on PortA and PortB (ie. up to 32bit R2R) – see my previous post.. :)
It requires to write a sketch for generating the DAC sample’s “source code” sequence (writing the sketch is left as an exercise to the OP)..
Vassilis
Sat Feb 03, 2018 3:39 pm
Example sketch for using the 12-bit MCP4921 DAC
viewtopic.php?f=18&t=3187&p=40871#p40871

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