{"id":10,"date":"2015-11-07T21:22:00","date_gmt":"2015-11-07T21:22:00","guid":{"rendered":""},"modified":"2023-08-18T12:34:41","modified_gmt":"2023-08-18T11:34:41","slug":"pwm-to-esc-converter-1","status":"publish","type":"post","link":"https:\/\/blog.hslracing.com\/electronics\/2015\/11\/pwm-to-esc-converter-1.html","title":{"rendered":"PWM to ESC Converter 1"},"content":{"rendered":"

I have been looking at ways of using the PWM output of GRBL<\/a> to control a brushless RC motor via an ESC.<\/p>\n

Now there is a commercial option available from Logicnc<\/a>, but I object to paying $34.99 for something that can potentially be made for pennies.<\/p>\n

I came across a post by Kretov on the CNCZone<\/a>\u00a0covering this very topic.<\/p>\n

He had posted a schematic and hex files, along with source code to implement this on a PIC12F629<\/a>\u00a0(DIP 8) chip.<\/p>\n

\"\"<\/a><\/div>\n

He even posted a suitable PCB layout.<\/p>\n

\"\"<\/a><\/div>\n

I also came across a similar post by Tweakie<\/a> on the\u00a0OpenBuilds<\/a>\u00a0website which discusses exactly the same type of process, again with hex files for use on a PIC micro-controller.<\/p>\n

\"\"<\/a><\/div>\n

His implementation uses NAND gates to provide buffering and a clean square wave, and is further enhanced with the provision for manual control via a potentiometer.<\/p>\n

Now I have nothing against PIC chips, especially as Microchip<\/a> are willing to give away free samples of their micro controllers, which is more than can be said for Atmel<\/a>, I just have yet to become familiar with their associated programming environment.<\/p>\n

As such I decided to attempt to port the code written by Kretov to a suitable AVR chip.<\/p>\n

My first choice, given the limited number of pins required (3), was to use an ATtiny25\/45\/85<\/a> (DIP8) chip, unfortunately, this has 2 x 8 bit timers, and this project calls for 1 x 8 bit and 1 x 16 bit timer or ideally 2 x 16 bit timers.<\/p>\n

So the next size up is the ATtiny24\/44\/84<\/a> (DIP 16) family, where it does indeed have the required timers.<\/p>\n

Unfortunately, \/16 is not an available prescaler for the 8 bit timer and so I had to make use of \/64 instead.<\/p>\n

This is still a work in progress and has yet to be tested, but I believe I now have a useable set of code:<\/p>\n

\/\/ 8 bit Timer 0 and \/64 prescaler used for input, 125 ticks = 1ms\r\n\/\/ 16 bit Timer 1 and \/8 prescaler used for output, 1000 ticks = 1ms\r\n\/\/ PWM input connected to PA0 (Pin 13)\r\n\/\/ ESC output connected to PB0 (Pin 2)<\/pre>\n
uint16_t MIN_WIDTH = 125; \/\/ 8MHz \/8 = 1000 clock ticks = 1ms
\nuint16_t MAX_LENGTH = 125; \/\/ 8MHz \/8 = 1000 clock ticks = 1ms
\nuint16_t OUT_PERIOD = 1000; \/\/ 8MHz \/16 = 16000 clock ticks = 20ms
\nuint16_t MAX_WIDTH = MIN_WIDTH + MAX_LENGTH; \/\/ 2ms
\nuint16_t InPeriod = 0;
\nvolatile uint16_t Pulse = MIN_WIDTH; \/\/ 1ms<\/p>\n
void setup(void)
\n{
\n\/\/ Setup Interrupts
\nGIMSK |= (1 << PCIE1); \/\/ Enable Interrupts on Pin Change
\nPCMSK0 |= (1 << PCINT0); \/\/ Generate Interrupts on PA0 (Pin 13)
\nsei(); \/\/ enable interrupts<\/p>\n
\/\/ Setup Timer 0
\nTCCR0B |= (1 << CS00) | (1 << CS01); \/\/ \/64 prescaler on Timer 0
\nTCNT0 = 0; \/\/ Initialise counter for Timer 0<\/p>\n
\/\/ Setup Timer 1
\nTCCR1B |= (1 << CS11); \/\/ \/8 prescaler on timer 1
\nTIFR1 |= (1 << ICF1); \/\/ clear interrupt-flag
\nTIMSK1 |= (1 << ICIE1); \/\/ enable Timer1 input capture interrupt
\nTCNT1 = 0; \/\/ Initialise counter for Timer 1<\/p>\n
\/\/ Setup Ports
\nDDRB |= (1 << DDB0); \/\/ enable port B0 (pin 2) for output<\/p>\n
CalcOutput(); \/\/ arm ESC
\n}<\/p>\n
void CalcOutput() { \/\/ calculate Timer 1 overflow based on Pulse
\nuint16_t i = 0xFFFF;<\/p>\n
if (PINB & (1 << PINB0)) { \/\/ last input low
\ni -= OUT_PERIOD – Pulse; \/\/
\n} else { \/\/ last input high
\ni -= Pulse;
\n}
\nTCNT1 = i;
\n}<\/p>\n
ISR (PCINT0_vect) {
\nif (TOV1 == 0b1) { \/\/ Timer 1 wrapped
\nPORTB ^= (1 << 0); \/\/ Flip Port B0
\nCalcOutput();
\nTIFR1 &= ~(1 << TOV1); \/\/ Reset Timer 1 Overflow flag
\n}<\/p>\n
if (PCINT0 == 0b1) { \/\/ Input pin data changed
\nif (PINA & (1 << PINA0)) { \/\/ last input high
\nInPeriod = TCNT1; \/\/ Period = timer count
\nTCNT1 = 0; \/\/ Reset Timer Count
\n} else {
\nif (InPeriod > 0) { \/\/ don’t calculate on first run through
\nPulse = MAX_WIDTH + MAX_LENGTH * TCNT0 \/ InPeriod; \/\/ re-scale output
\nif (Pulse > MAX_WIDTH) Pulse = MAX_WIDTH;
\nif (Pulse < MIN_WIDTH) Pulse = MIN_WIDTH;
\n}
\n}
\n}<\/p>\n
if (TOV0 == 0b1) { \/\/ Timer 0 wrapped – no pulses detected
\nif (PINA & (1 << PINA0)) { \/\/ last input high
\nPulse = MAX_WIDTH; \/\/ max pulse
\n} else { \/\/ last input low
\nPulse = MIN_WIDTH; \/\/ min pulse
\n}
\nInPeriod = 0; \/\/ Reset Period
\nTIFR0 &= ~(1 << TOV0); \/\/ Reset Timer 0 overflow flag
\n}
\n}<\/p>\n
void loop() { \/\/ Do Nothing – all handled in ISR
\n}<\/p>\n","protected":false},"excerpt":{"rendered":"
I have been looking at ways of using the PWM output of GRBL to control a brushless RC motor via an ESC. Now there is a commercial option available from Logicnc, but I object to paying $34.99 for something that can potentially be made for pennies. I came across a post by Kretov on the…<\/p>\n","protected":false},"author":2,"featured_media":55,"comment_status":"open","ping_status":"open","sticky":false,"template":"","format":"standard","meta":{"footnotes":""},"categories":[1],"tags":[],"class_list":["post-10","post","type-post","status-publish","format-standard","has-post-thumbnail","hentry","category-uncategorised"],"_links":{"self":[{"href":"https:\/\/blog.hslracing.com\/electronics\/wp-json\/wp\/v2\/posts\/10","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/blog.hslracing.com\/electronics\/wp-json\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/blog.hslracing.com\/electronics\/wp-json\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/blog.hslracing.com\/electronics\/wp-json\/wp\/v2\/users\/2"}],"replies":[{"embeddable":true,"href":"https:\/\/blog.hslracing.com\/electronics\/wp-json\/wp\/v2\/comments?post=10"}],"version-history":[{"count":4,"href":"https:\/\/blog.hslracing.com\/electronics\/wp-json\/wp\/v2\/posts\/10\/revisions"}],"predecessor-version":[{"id":179,"href":"https:\/\/blog.hslracing.com\/electronics\/wp-json\/wp\/v2\/posts\/10\/revisions\/179"}],"wp:featuredmedia":[{"embeddable":true,"href":"https:\/\/blog.hslracing.com\/electronics\/wp-json\/wp\/v2\/media\/55"}],"wp:attachment":[{"href":"https:\/\/blog.hslracing.com\/electronics\/wp-json\/wp\/v2\/media?parent=10"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/blog.hslracing.com\/electronics\/wp-json\/wp\/v2\/categories?post=10"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/blog.hslracing.com\/electronics\/wp-json\/wp\/v2\/tags?post=10"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}