I'm trying to use a cheaper smaller ATtiny24 rather than eg ATmega48 (approx $1.00 vs $2.50 for >10)
I need 4 digital in (to set the mode), and 8ADC + 4 digital out while running. The ATtiny has 8ADC + 4Dig.
So, can I do something (with diodes and other stuff maybe ??) so that when I press the reset button the sketch first reads the input mode from 4 dip switches attached to 4 digital pins. And then the main loop uses those pins as outputs (and the output state isn't affected by the dip switch positions) ?
The output will be simulating a switch input by taking the level to ground. Will be used as input to eg an old arcade pcb or eg a keyboard encoder such as an i-pac.
/*
Demonstration how to use a pin as a output for a LED
and as an input for a switch.
Note:
The LED 'must' be connected to +5V through a 470 ohm (or larger) resistor.
The switch is connected to GND through a 220 ohm resistor.
Version YY/MM/DD
1.00 16/12/11 Running code
*/
//**********************************************************************
//G l o b a l v a r i a b l e s
//**********************************************************************
const byte heartLED = 13; //Heart beat LED, toggles on and off showing if there is blocking code
const byte Pin12LED = 12; //Push ON push OFF, controlled by a switch on pin 6
const byte SwitchLED = 6; //Switch and LED connected this pin, switch pushed = LOW
//LED is toggled showing the dual action of this pin
//SRAM variables
byte state = 1;
byte lastSwitchState = 1;
unsigned long Pin13Millis;
unsigned long Pin6Millis;
unsigned long SwitchMillis;
// s e t u p ( )
//**********************************************************************
void setup()
{
//**************************************
digitalWrite(heartLED, HIGH); //LOW = ON
pinMode(heartLED, OUTPUT);
digitalWrite(Pin12LED, HIGH); //LOW = ON
pinMode(Pin12LED, OUTPUT);
digitalWrite(SwitchLED, HIGH); //LOW = ON
pinMode(SwitchLED, OUTPUT); //normal state of this pin
} // >>>>>>>>>>>>>>>>>> E N D O F s e t u p ( ) <<<<<<<<<<<<<<<<<<<<<
// l o o p ( )
//**********************************************************************
void loop()
{
//***************************
//HeartBeat LED
if (millis() - Pin13Millis >= 100UL)
{
Pin13Millis = millis();
//Toggle heartLED
digitalWrite(heartLED, !digitalRead(heartLED));
}
//***************************
if (millis() - Pin6Millis >= 500ul)
{
Pin6Millis = millis();
//Toggle the LED on the SwitchLED pin
digitalWrite(SwitchLED, !state);
state = !state;
}
//***************************
//None blocking code goes here
//***************************
//time to check the Switch(s)?
if (millis() - SwitchMillis >= 50ul)
{
SwitchMillis = millis();
handleSwitchPresses();
}
} // >>>>>>>>>>>>>>>>>>> E N D O F l o o p ( ) <<<<<<<<<<<<<<<<<<<<<<
//======================================================================
// F U N C T I O N S
//======================================================================
// h a n d l e S w i t c h P r e s s e s( )
//**********************************************************************
void handleSwitchPresses()
{
//**** R e a d i n g t h e s w i t c h s h a r e d w i t h L E D ****
//Reading the switch takes ~14us
//save the condition of the output pin
byte PinState = digitalRead(SwitchLED);
//read the switch connected to this pin
pinMode(SwitchLED, INPUT_PULLUP);
byte switchPosition = digitalRead(SwitchLED);
//return the pin to OUTPUT
pinMode(SwitchLED, OUTPUT);
//restore the pin state
digitalWrite(SwitchLED, PinState);
//**** R e a d i n g t h e s w i t c h s h a r e d w i t h L E D ****
//has the SwitchLED changed state?
if (switchPosition != lastSwitchState)
{
lastSwitchState = switchPosition;
if (switchPosition == LOW) //do LOW stuff
{
//toggle Pin12LED
digitalWrite(Pin12LED, !digitalRead(Pin12LED));
}
else //do HIGH stuff
{
}
} //END of SwitchLED changed state
//Other Switches
} // E n d o f h a n d l e S w i t c h P r e s s e s ( )
//**********************************************************************
//======================================================================
// E N D O F C O D E
//======================================================================
The LEDs represent the devices you need to control. Note that they can only be loads connected to the supply or a high impedance as they must not pull down against INPUT_PULLUP.
Similarly the protective resistors in series with the DIP switches must be substantially less (at very minimum, half the value) than the LED resistors because the DIP switches must be able to pull the load sufficiently LOW to be correctly read. OTOH, their minimum value of 240 Ohms is chosen so that the pin when set to output HIGH is not overloaded.
Thus the value of 240 Ohms (I would say 330) for the switch resistors and 1k2 for the LED resistors.
You must remember there is a short interval when the pin is an input and a much longer period when the pin is an output.
This should be taken into consideration in your project.
To repeat, here is a read when the pin is at output LOW and the switch was open/HIGH during the read time, hence the short positive pulse.
If the pin was at output HIGH and the switch was closed, you would see an inverted image of what’s seen above.
Now another Arduino - or similar, or a CMOS logic gate - is (or should be) a high impedance. You do not need a pull-up as to read the DIP switch, INPUT_PULLUP will generally pull up quite well and when the pin becomes an OUTPUT, its state will be strictly controlled as HIGH or LOW.
If however there was a long cable between the two, you may want a stronger pull-up than INPUT_PULLUP provides in order to account for leakage and interference pickup in the wiring.
I could, but there are many other strands needing my attention at the same time. eg I don't know if I can get custom PCBs with ATTINYx4 on them. JLCPCB says no stock even though their parts supplier has them. More stuff I don't understand!
