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Simple Arduino script to set pins high, low, input, pull up, or analog/servo, clock in or out data, with timing/start/stop, and read all or a single pin back via serial IO.
Simple Arduino script to set pins high, low, input, pull up, or analog/servo,
clock out data with timing, and read all or a single pin back via serial IO.
Written for the TinyDuino in the end effector of the
Dexter robot from, but generally useful to turn the Arduino
into a tool for generating test signals, and reading back results. Not as
powerful as the busPirate, but more flexible in some ways and much easier to
operate. Not a replacement for Firmata as this is intended to be used by a
human directly via serial monitor or terminal, not from a program.
#? //return binary value of digital pin, and value for analog input if exists
//if # and #, are zero, returns all pins and analog values at once. e.g. ?
#I //set pin # to an input. e.g. 3I
#P //set pin # to an input with internal pullup. 4P
#H //set pin # to a high output. 3H4H
#L //set pin # to a low output. 5L4L3L
#D //delay # microseconds between each command, with a minimum of about 47uS
#, //save pin # as the default pin for all commands e.g. 3,HLHLHL
#A //set pin # to an analog output with value. Only PWM outputs will respond.
// use with , command e.g. 5,120A will put 120 on pin 5
#S //Set Timer1,2 divide mode. Default 4S=244Hz, 5S is 122Hz on 3,11 61Hz on 9,10
//has no effect on Timer0 pins 5 and 6, they stay at 244Hz
_- //low high clocked puts out the set of low and high signals shown on # with
// a clock on #, e.g. 5,11-__-_--_ clocks out 10010110 on pin 11, with clock
// pulses on pin 5. Clock is currently falling edge only.
. //reads data back from # while clocking #,
// e.g. 5L 11H 5,11-__-_--_. ......... clocks out 10010110, gets the ack, and
// then 8 bits of data and a final ack.
( //I2C start with # as SDA and #, as SCL
) //I2C stop with # as SDA and #, as SCL. Pins left floating pulled up.
// e.g. 5,11(-__-_--_. .........) starts, 10010110, gets ack, data, ack, stop
Commands can be strung together on one line; spaces, tabs, carrage returns and line feeds
are all ignored. If no n is specified, value previously saved by , is used.
//returns something like: <10000000001111,539,475,425,408,386,376>
// where 10000000001111 shows the binary value of each pin, from 0 to 14. Pin 0 is 1
// 539,475,425,408,386,376 are the values read from each analog channel 0 to 5
//returns something like: <1:1,539> where 1 is the binary value of pin 1 and
//539 is the analog value of channel 1
//returns something like <6:0> which is the value of pin 6 (no analog)
4L 6H 5,120A
//(nothing returned) Drives pin 4 low, pin 6 high and puts a PWM / Analog value of 120 on pin 5
//this also saves pin 5 as the default pin for all commands from now on
//(nothing returned) assuming prior command was 5,120A put 240 out pin 5 as new analog value
5S 3,100A
//(nothing returned) The normal PWM output is 244Hz which is a bit to fast for servoes.
//The S command sets the divisor for Timer1 and Timer2. 4S is the default, 5S drops the frequency
//of pins 3 and 11 to 122Hz and pins 9 and 10 to 61Hz allowing servos to work just fine.
//After 5S, 47A is center with a 1.5mS pulse width, 31A 0.5mS or far CCW, 62A is 2mS; far CW.
//So this only allows 62-31 or about 30 steps for 90' or 3' resolution. For many jobs, it's enough.
//assuming 5, has been recieved before, returns just the value of pin 5 and analog 5
//(nothing returned) clears saved pin, ? now returns all pins.
//(nothing returned) delay is 1 millisecond between commands. So pin 5 pulse 3 times at ~200Hz
//Actually about 1.04mS because of the time it takes to recieve and interpret each command.
//The delay command is also useful for making sure all the commands on a line arrive before they are
//excecuted. e.g.:
10000D 3D 5,LHLHL?
//will put out 2 pulses at 50uS per pulse or 10KHz without the 10000D, they are 163uS
//The time it takes to interpret a command is about 47uS so 3D makes it 50. For 100uS
//53D would work. Take the uS delay you want and subtract 47.
//With larger delays, the error is consistant but has relativly less effect.
// Note that the CYCLE_DELAY is not used as long as new characters are available.
#define ANALOG_PINS 6
#define DIGITAL_PINS 14
#define BAUD_RATE 57600
//didn't work at 115200
#define CYCLE_DELAY 100
unsigned long n,p,d;
char cmd;
Pins 9 and 10 run at 31250Hz from Timer1 which is only used for servo.
3 and 11 are on Timer2, 5 and 6 on Timer0. These are also used for delay, millis, etc...
So limiting our changes to Timer1 and pins 9 and 10 allows us to still have timing.
switch(divisor) {
case 1: mode = 0x01; break; //31250Hz
case 8: mode = 0x02; break; //3906.25Hz
case 64: mode = 0x03; break; //488.28125Hz //default?
case 256: mode = 0x04; break; //122.0703125Hz
case 1024: mode = 0x05; break;//30.517578125Hz
TCCR1B = TCCR1B & 0b11111000 | mode;
Says only Timer0 is used for delay and millis...
We can try changing 3 and 11 on Timer2
Different divisors, so compensate
T2 T1 / Freq
0x01 1 1 31250
0x02 2 8 3906.25
0x03 2 32 976.5625
0x04 3 64 488.28125 //default?
0x05 3 128 244.140625
0x06 4 256 122.0703125
0x07 5 1024 30.517578125
TCCR2B = TCCR2B & 0b11111000 | mode;
if (n>2) n--; //1,2,2,3,4,5,6
if (n>3) n--; //1,2,2,3,3,4,5
formula is f = clock / (510 * mode) where clock=16MHz
If you mess with TCCR0B, delay can be compensated as follows
0x01: delay(64000) or 64000 millis() ~ 1 second
0x02: delay(8000) or 8000 millis() ~ 1 second
0x03: delay(1000) or 1000 millis() ~ 1 second //default
0x04: delay(250) or 250 millis() ~ 1 second
0x05: delay(62) or 62 millis() ~ 1 second
(Or 63 if you need to round up. The number is actually 62.5)
void setPin9_10PWMFreq(freq) {
void delayus(unsigned long us) {
if (us>10000) { //can't delayMicroseconds() more than 16838
us=us % 10000;
void setup() {
n=0; //number
p=0; //pin number
d=2; //delay. Default is 2uS or 250KHz
void loop(){
while (Serial.available() > 0) { //if data has arrived
int c =; //get the data
if ('0' <= c && c <= '9') { //if it's a digit
n = (c-'0') + n*10; //add it to n, shift n up 1 digit
continue; //and loop
cmd = char(c); //wasn't a number, must be a command
if (' '==cmd || '\t'==cmd) { continue;} //whitespace does nothing
if (','==cmd) { p=n; n=0; continue;} //save n to p, clear n, loop
if (0==n) {n=p; } //if we don't have a value, use the prevous pin number
switch (cmd) {
case '?': //get information
Serial.print("<"); //optional, just to signal start of data
if (0==n) { //if we didn't have a number selecting a pin
for (int p = 0; p < DIGITAL_PINS; p++) { //get all the pins
//n = digitalRead(p) + n<<1; //convert to binary number
Serial.print(digitalRead(p));//and also print.
//Serial.print(n); //print the binary value of all pins
for (int p = 0; p < ANALOG_PINS; p++) { //also check all the analog
else {
Serial.print(digitalRead(n)); //just that one pin
if (ANALOG_PINS > n) { //if there is an analog channel
Serial.print(analogRead(p)); //also return it
case '-':
case 'H': //set pin n output high
case '_':
case 'L': //set pin n output low
case 'I': //set pin n input
case 'P': //set pin n input with pullup
case '.': //clock in data from n via p
pinMode(n,INPUT_PULLUP); //make n input with pull now
case '(': //I2C start, data low while clock high
digitalWrite(n,HIGH); //data high
pinMode(p,OUTPUT); //setup clock (if not already)
digitalWrite(p,HIGH); //send clock high
delayus(d); //wait
digitalWrite(n,LOW); //data low
delayus(d); //wait
digitalWrite(p,LOW); //send clock low
continue; //no further processing
case ')': //I2C stop, data low while clock high
pinMode(n,OUTPUT); //data may be floating high (input from slave)
digitalWrite(n,LOW); //so we need to drive it low
pinMode(p,OUTPUT); //setup clock (if not already)
digitalWrite(p,LOW); //send clock high
pinMode(p,INPUT_PULLUP); //clock floats high
pinMode(n,INPUT_PULLUP); //data floats high
continue; //no further processing
case 'A': //set pin p to analog output value n
case 'D': //delay n ms per instruction
case 'S': //PWM speed 5 allows servos, 4 is default.
TCCR2B = TCCR2B & 0b11111000 | n; // Timer2, pins 3 and 11
if (n>2) n--; //1,2,2,3,4,5,6
if (n>3) n--; //1,2,2,3,3,4,5
TCCR1B = TCCR1B & 0b11111000 | n; // Timer1, pins 9 and 10
case '\n':
case '\r':
n=0; cmd=0; //clear command and value at end of line.
continue; //loop now, no delay
break; //shouldn't get here
if ('0'>cmd || '_'==cmd) {//was it punctuation?
digitalWrite(p,HIGH); //raise the clock
delayus(d/2); //half delay
if ('.'==cmd) {Serial.print(digitalRead(n));}
digitalWrite(p,LOW); //drop the clock
delayus(d/2); //half delay
else {
n=0; //zero out value for next command.
delayus(d); //wait a bit for the next cycle.
//p is NOT cleared, so you can keep sending new commands only
cmd=0; //done with command.

JamesNewton commented May 13, 2017 edited

To use with a Dexter first SSH in, or from most *nix systems at the command line setup the port speed.
stty -F /dev/ttyUSB0 ospeed 57600 ispeed 57600 raw

To test, just send a ? with:
echo -ne '?' > /dev/ttyUSB0
and then listen for a response with:
cat -v < /dev/ttyUSB0
you should get something like:
in return. If you just want to "have a conversation" with it, you can try:
cat /dev/ttyUSB0 & cat > /dev/ttyUSB0
Then type commands to set pins high or low or to a PWM duty cycle and read them with or without pull up. Press Ctrl Z to get out.


JamesNewton commented May 17, 2017 edited

3rd version:

  • Change timing from millisecond to microsecond... yes, it can't really do command in 1 uS (47uS overhead, so 3D is 50uS) but this allows sub millisecond timing down to 50uS so that is quite useful. This required that all the internal variables become longs because 1 second is 1000000D. Unsigned because we don't do negative.
  • Added ability to clock in data as well as out. Data read is a bit slower than write because of the time to transmit the character.
  • Added I2C start and stop commands. e.g. 5,11(-__-_--_. ........ .) starts with clock on pin 5 and data on 11, sends 10010110, gets ack, data, ack, and stops. It returns the data as binary. It might be nice to return the data as a decimal value in addition to the binary, but I would have to use something to separate out acks and data. Maybe space?
  • Multiple bug fixes. Space /really/ does nothing now. Clock pulses go up /after/ the data.
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