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New to PIC programming or just programming in general. Wondering how I can display a number on the 7 segment display that corresponds to the number of times the push button at RA5 is pressed. E.g press button 2 times = number 2 displayed and if it's pressed 10 times, the count resets to 0. Any help is appreciated
What do you mean this question is too broad?
Tom, first off, to help you out in the future:
According to the "closed" info. box on the question, this question was closed because it "needs to be more focused", and it should be updated "so it focuses on one problem only." I'd like to help you know what that means from my perspective.
I didn't vote to close it, but in this case I totally understand why it was closed.
It's too broad. You showed no coding attempt whatsoever and you asked what you thought was a very focused question, but which actually is too broad because there is too much to cover here. With you writing no code whatsoever, the questions within your question might include the following:
How do you write C at all?
How do you set up a main() function?
What's a function?
What's a variable?
What's a signed vs unsigned variable?
How do you do bare-metal multi-tasking?
How do you program a PIC microcontroller?
What are hardware registers and how do you use them?
How do you configure pins as inputs vs outputs?
How do you read pin states?
How do you write to pins?
How do you do bitwise operations to set an entire output port (all pins to the display) all at once instead of one-at-a-time?
How does electricity work?
What does it mean to write a pin to output LOW vs ouput HIGH vs input?
What's a pullup resistor?
What's an LED array? How do you drive one?
Are the LEDs in the 7-segment display turned on by writing the pin to output HIGH or output LOW (ie: do we need to source from or sink to the pins to light up the LEDs)?
How do displays work and how do you control them?
I originally didn't see the circuit diagram until I edited the question to make the image show up, so I at first I also needed this information and thought we may need to cover the following:
Does the 7-segment display have its own on-board driver IC and require I2C, SPI, or asynchronous RS-232-style TTL logic level Serial commands to drive it instead?
How do displays work and how do you control them?
What is Persistence of Vision (PoV) and how might it apply?--in particular if driving multiple digits (multiple 7-segment displays)
Do we need to consider multiplexing so you can control more 7-Segment digits with fewer pins?
Do we need to consider Charlieplexing to use fewer pins still than standard multiplexing?
Anyway, let me get you started. The concept for your circuit is pretty straightforward.
Here is how your circuit works:
Each segment on the display is turned on by setting the appropriate pin to output LOW, since Vcc (probably 5V) is connected to the other side of the LEDs. So, to turn on segment a, you'd set RC0 to output LOW, to turn on segment b, you'd set RC1 to output LOW, etc. Since all of your LEDs in this display share a common Vcc (usually 5V) pin, this is a common anode 7-segment display. Since each of the 7 LEDs in the display has its own dedicated pin, you can light up any of the LEDs at one time, rather than having to round-robbin through them in a multiplexed or Charliplexed fashion.
If you wish to add another digit (another 7-segment display), you can double the number of required pins from 7 to 14, OR you can multiplex the new display, moving Vcc of each display to its own pin, and sharing the 7 segment pins RC0 through RE2. Therefore, 2 displays can take 14 pins if not multiplexed, or 9 pins if multiplexed. OR, if you have a common-anode and a common-cathode 7-segment display, you can Charlieplex them, hooking up each individual LED together and the common anode of one display and the common cathode of the other display together on another pin, thereby getting away with only 8 pins for 2 displays--the direction of current would set which display gets lit up. Round-robbining through the displays to refresh them, thereby relying on our eyes' persistence of vision trait, would be required for both multiplexing and Charlieplexing.
You read the RA5 button presses by seeing when RA5, an input pin, goes LOW. Since the button grounds the pin, and the pin has an external pullup resistor on it, HIGH means the button is NOT pressed, and LOW means it is pressed. Be sure to debounce this button press in software or else a single button press may register as dozens or even hundreds of button presses, depending on the mechanics of the button.
That's the circuit.
Here is how the program logic works:
The logic is pretty straightforward too: each time you read a debounced button press, increment a counter. Output the digit on the 7-segment display according to the counter. Example: to write a 2, you'd turn on segments a, b, g, e, and d. You can look at the display to figure out the other numbers.
Sample source code outline to get you started:
#include <stdbool.h> // For `true` (`1`) and `false` (`0`) macros in C
#include <stdint.h> // For `uint8_t`, `int8_t`, etc.
// Read the pin to look for button presses and return true if the
// **debounced** button changes indicate the button has been pressed once
bool buttonWasPressedOnce()
{
// you do this
}
// Write a number 0 to 9 to the display
void writeDisplay(uint8_t number)
{
// you do this
}
// set up your PIC peripherals, input/output pin states, etc, here
void setup()
{
// you do this
}
// your main program logic goes here; this runs repeatedly, forever
void loop()
{
static uint8_t button_pressed_count = 0;
if (buttonWasPressedOnce())
{
button_pressed_count++;
// roll over after 9 back to 0
if (button_pressed_count > 9)
{
button_pressed_count = 0;
}
}
writeDisplay(button_pressed_count);
}
int main()
{
setup();
while (true)
{
loop();
}
return 0;
}
References and additional reading, including sample libraries to look at:
Here is some Arduino code to get you started, to see various options. Port it to your PIC microcontroller: https://www.instructables.com/Different-methods-of-driving-7-Segment-LED-display/
Sample library to study as a reference: https://github.com/DeanIsMe/SevSeg
You'll also need to know button debouncing, and a ton of other skills. Example debouncing: https://www.arduino.cc/en/Tutorial/BuiltInExamples/Debounce
my own debounce library I wrote for Arduino a long time ago: https://www.electricrcaircraftguy.com/2014/05/ercaguybuttonreader-library-for-arduino.html and https://github.com/ElectricRCAircraftGuy/eRCaGuy_ButtonReader and https://github.com/ElectricRCAircraftGuy/eRCaGuy_EventReader
https://www.allaboutcircuits.com/technical-articles/driving-led-arrays-with-an-arduino/
https://www.google.com/search?q=led+array&oq=led+array&aqs=chrome..69i57j69i65.2207j0j7&sourceid=chrome&ie=UTF-8
https://www.sparkfun.com/products/retired/13795
great video: https://www.youtube.com/watch?v=ohewJ9sTfwM
https://en.wikipedia.org/wiki/Multiplexed_display
https://en.wikipedia.org/wiki/Charlieplexing
https://en.wikipedia.org/wiki/Three-state_logic
https://en.wikipedia.org/wiki/Persistence_of_vision
https://en.wikipedia.org/wiki/Seven-segment_display
I came across this code by Ganssle regarding switch debouncing. The code seems pretty efficient, and the few questions I have maybe very obvious, but I would appreciate clarification.
Why does he check 10 msec for button press and 100 msec for button release. Can't he just check 10 msec for press and release?
Is polling this function every 5 msec from main the most effecient way to execute it or should I check for an interrupt in the pin and when there is a interrupt change the pin to GPI and go into the polling routine and after we deduce the value switch the pin back to interrupt mode?
#define CHECK_MSEC 5 // Read hardware every 5 msec
#define PRESS_MSEC 10 // Stable time before registering pressed
#define RELEASE_MSEC 100 // Stable time before registering released
// This function reads the key state from the hardware.
extern bool_t RawKeyPressed();
// This holds the debounced state of the key.
bool_t DebouncedKeyPress = false;
// Service routine called every CHECK_MSEC to
// debounce both edges
void DebounceSwitch1(bool_t *Key_changed, bool_t *Key_pressed)
{
static uint8_t Count = RELEASE_MSEC / CHECK_MSEC;
bool_t RawState;
*Key_changed = false;
*Key_pressed = DebouncedKeyPress;
RawState = RawKeyPressed();
if (RawState == DebouncedKeyPress) {
// Set the timer which will allow a change from the current state.
if (DebouncedKeyPress) Count = RELEASE_MSEC / CHECK_MSEC;
else Count = PRESS_MSEC / CHECK_MSEC;
} else {
// Key has changed - wait for new state to become stable.
if (--Count == 0) {
// Timer expired - accept the change.
DebouncedKeyPress = RawState;
*Key_changed=true;
*Key_pressed=DebouncedKeyPress;
// And reset the timer.
if (DebouncedKeyPress) Count = RELEASE_MSEC / CHECK_MSEC;
else Count = PRESS_MSEC / CHECK_MSEC;
}
}
}
Why does he check 10 msec for button press and 100 msec for button release.
As the blog post says, "Respond instantly to user input." and "A 100ms delay is quite noticeable".
So, the main reason seems to be to emphasize that the make-debounce should be kept short so that the make is registered "immediately" by human sense, and that the break debounce is less time sensitive.
This is also supported by a paragraph near the end of the post: "As I described in the April issue, most switches seem to exhibit bounce rates under 10ms. Coupled with my observation that a 50ms response seems instantaneous, it's reasonable to pick a debounce period in the 20 to 50ms range."
In other words, the code in the example is much more important than the example values, and that the proper values to be used depends on the switches used; you're supposed to decide those yourself, based on the particulars of your specific use case.
Can't he just check 10 msec for press and release?
Sure, why not? As he wrote, it should work, even though he wrote (as quoted above) that he prefers a bit longer debounce periods (20 to 50 ms).
Is polling this function every 5 msec from main the most effecient way to execute it
No. As the author wrote, "All of these algorithms assume a timer or other periodic call that invokes the debouncer." In other words, this is just one way to implement software debouncing, and the shown examples are based on a regular timer interrupt, that's all.
Also, there is nothing magical about the 5 ms; as the author says, "For quick response and relatively low computational overhead I prefer a tick rate of a handful of milliseconds. One to five milliseconds is ideal."
or should I check for an interrupt in the pin and when there is a interrupt change the pin to GPI and go into the polling routine and after we deduce the value switch the pin back to interrupt mode?
If you implement that in code, you'll find that it is rather nasty to have an interrupt that blocks the normal running of the code for 10 - 50ms at a time. It is okay if checking the input pin state is the only thing being done, but if the hardware does anything else, like update a display, or flicker some blinkenlights, your debouncing routine in the interrupt handler will cause noticeable jitter/stutter. In other words, what you suggest, is not a practical implementation.
The way the periodic timer interrupt based software debouncing routines (shown in the original blog post, and elsewhere) work, they take only a very short amount of time, just a couple of dozen cycles or so, and do not interrupt other code for any significant amount of time. This is simple, and practical.
You can combine a periodic timer interrupt and an input pin (state change) interrupt, but since the overhead of many of the timer-interrupt-only -based software debounces is tiny, it typically is not worth the effort trying to combine the two -- the code gets very, very complicated, and complicated code (especially on an embedded device) tends to be hard/expensive to maintain.
The only case I can think of (but I'm only a hobbyist, not an EE by any means!) is if you wanted to minimize power use for e.g. battery powered operation, and used the input pin interrupt to bring the device to partial or full power mode from sleep, or similar.
(Actually, if you also have a millisecond or sub-millisecond counter (not necessarily based on an interrupt, but possibly a cycle counter or similar), you can use the input pin interrupt and the cycle counter to update the input state on the first change, then desensitize it for a specific duration afterwards, by storing the cycle counter value at the state change. You do need to handle counter overflow, though, to avoid the situation where a long ago event seems to have happened just a short time ago, due to counter overflowing.)
I found Lundin's answer quite informative, and decided to edit my answer to show my own suggestion for software debouncing. This might be especially interesting if you have very limited RAM, but lots of buttons multiplexed, and you want to be able to respond to key presses and releases with minimum delay.
Do note that I do not wish to imply this is "best" in any sense of the world; I only want you to show one approach I haven't seen often used, but which might have some useful properties in some use cases. Here, too, the number of scan cycles (milliseconds) the input changes are ignored (10 for make/off-to-ON, 10 for break/on-to-OFF) are just example values; use an oscilloscope or trial-and-error to find the best values in your use case. If this is an approach you find more suitable to your use case than the other myriad alternatives, that is.
The idea is simple: use a single byte per button to record the state, with the least significant bit describing the state, and the seven other bits being the desensitivity (debounce duration) counter. Whenever a state change occurs, the next change is only considered a number of scan cycles later.
This has the benefit of responding to changes immediately. It also allows different make-debounce and break-debounce durations (during which the pin state is not checked).
The downside is that if your switches/inputs have any glitches (misreadings outside the debounce duration), they show up as clear make/break events.
First, you define the number of scans the inputs are desensitized after a break, and after a make. These range from 0 to 127, inclusive. The exact values you use depend entirely on your use case; these are just placeholders.
#define ON_ATLEAST 10 /* 0 to 127, inclusive */
#define OFF_ATLEAST 10 /* 0 to 127, inclusive */
For each button, you have one byte of state, variable state below; initialized to 0. Let's say (PORT & BIT) is the expression you use to test that particular input pin, evaluating to true (nonzero) for ON, and false (zero) for OFF. During each scan (in your timer interrupt), you do
if (state > 1)
state -= 2;
else
if ( (!(PORT & BIT)) != (!state) ) {
if (state)
state = OFF_ATLEAST*2 + 0;
else
state = ON_ATLEAST*2 + 1;
}
At any point, you can test the button state using (state & 1). It will be 0 for OFF, and 1 for ON. Furthermore, if (state > 1), then this button was recently turned ON (if state & 1) or OFF (if state & 0) and is therefore not sensitive to changes in the input pin state.
In addition to the accepted answer, if you just wish to poll a switch from somewhere every n ms, there is no need for all of the obfuscation and complexity from that article. Simply do this:
static bool prev=false;
...
/*** execute every n ms ***/
bool btn_pressed = (PORT & button_mask) != 0;
bool reliable = btn_pressed==prev;
prev = btn_pressed;
if(!reliable)
{
btn_pressed = false; // btn_pressed is not yet reliable, treat as not pressed
}
// <-- here btn_pressed contains the state of the switch, do something with it
This is the simplest way to de-bounce a switch. For mission-critical applications, you can use the very same code but add a simple median filter for the 3 or 5 last samples.
As noted in the article, the electro-mechanical bounce of switches is most often less than 10ms. You can easily measure the bouncing with an oscilloscope, by connecting the switch between any DC supply and ground (in series with a current-limiting resistor, preferably).
I am trying to implement PWM LED dimming in 6 stages, where each stage in more bright, based on clicking button, which increments external pin, which serves the value to timer.
I am facing a problem, that sometimes, value variable is too large than it should be and skips some levels of brightness. For example, value increments: 1,2,3, then jumps to 6,7, etc.
Can anybody pinpoint where is the mistake I am making.
Here is the code:
//EDIT: code removed, because it is a school assignment
This looks like contact bouncing. When input is processed by the CPU, a simple way to solve it is to disable input for a certain duration after an event is detected. Since you directly control timer input from a button, you may not have much control. However, I would experiment with the ETF field of the SMCR register (which in your case is likely set by the sClockSourceConfig.ClockFilter field) and the clock divisor CKD of the CR1 register (which seems like htim2.Init.ClockDivision in your code) (sorry, I am not familiar with STM libraries).
I've been doing a little thermometer project to learn Arduino and there is an annoying thing that I have no idea how to resolve.
I have two push buttons to set Min and Max temperature and when I push the buttons it's supposed to set the Min and Max temperature on display.
The problem is that sometimes (50% of times) when I push the buttons during the reading of the temperature sensor, the buttons don't work. I press it but the Min/Max temperature are not set because Arduino is stuck in reading the temperature sensor.
Is there any trick to solve this kind of problem? If I had a keyboard for typing some number for example I imagine I would have the same problem and It's not "user-friendly".
Here is an example of part of the code I'm using:
#include <OneWire.h>
#include <DallasTemperature.h>
#include <LiquidCrystal.h>
//variables declaration...
void setup() {
sensors.begin();
sensors.getAddress(sensor1, 0);
pinMode(buzzer, OUTPUT);
pinMode(btBuzzer, INPUT);
pinMode(btMin, INPUT);
pinMode(btMax, INPUT);
}
void loop() {
readButtons();
playBuzzer();
readTemperature();
printDisplay();
delay(150);
}
void readButtons(){
if(digitalRead(btBuzzer)){
buzzerOn = !buzzerOn;
}
if(digitalRead(btMin)){
if(tempMin == 69)
tempMin = 59;
else
tempMin++;
}
if(digitalRead(btMax)){
if(tempMax == 75)
tempMax = 63;
else
tempMax++;
}
}
void readTemperature(){
sensors.requestTemperatures();
temperature = sensors.getTempC(sensor1);
}
//lots of other methods
As others have pointed out here, the button press may not happen at the same time as you query the pin with digitalRead(btBuzzer). This type of problem is what so called "interrupts" were invented for, which allow you to respond to events that may occur while you are not monitoring the pin of interest.
For example, the Arduino UNO R3 allow for interrupts on pin 2 and 3. You should look up the reference for attachInterrupt(). The processor will execute a callback function in the event (the "interrupt") that you register for (e.g. the voltage on pin 2 changing from low to high). This means that you will no longer have to call a readButtons() function from your main loop.
Some of the best ways to learn coding exist in how to answer this question.
What I'd like to suggest doing is to try timing your code. Remember that loop() is creating a repeating structure. So we can say things like how long does the computer take to run each loop. When we have an interrupt like a button press how does that effect the iteration through the loop and is it conditional about how to rest the processor (the delay).
The delay is required so as to not do what's called "spin" the processor (have the processor as quickly as it can do a lot of work to accomplish absolutely nothing). However, notice how the code doesn't account for work done changing how long we delay?
Now let's imagine the processor actually can go through that loop more than one time very quickly. Remember delay of only 150 milliseconds isn't a lot of time. So maybe one button press will be enough to set tempMin from 59 to 69 in rapid succession and loop several times over rather than just increasing one number at a time.
What you have here is a chance to learn debugging. First trick is to determine is the loop running too fast or too slow; are you getting desired functionality or not and finally if you can reask the question after you know if it's happening too fast or slow.
For now, I'd recommend taking a look at global variables and finite state machines (i.e. if you're in a state of button press, don't accept any further button presses until you're done with your state and only transition in known ways).
Im using C language for a PIC18F to produce tones such that each of them plays at certain time-interval. I used PWM to produce a tone. But I don't know how to create the intervals. Here is my attempt.
#pragma code //
void main (void)
{
int i=0;
// set internal oscillator to 1MHz
//OSCCON = 0b10110110; // IRCFx = 101
//OSCTUNEbits.PLLEN = 0; //PLL disabled
TRISDbits.TRISD7 = 0;
T2CON = 0b00000101; //timer2 on
PR2 = 240;
CCPR1L = 0x78;
CCP1CON= 0b01001100;
LATDbits.LATD7=0;
Delay1KTCYx(1000);
while(1);
}
When I'm doing embedded programming, I find it extremely useful to add comments explaining exactly what I'm intending when I'm set configuration registers. That way I don't have to go back to the data sheets to figure out what 0x01001010 does when I'm trying to grok the code the next time I have to change it. (Just be sure to keep the comments in sync with the changes).
From what I can decode, it looks like you've got the PWM registers set up, but no way to change the frequency at your desired intervals. There are a few ways to do it, here are 2 ideas:
You could read a timer on startup, add the desired interval to get a target time, and poll the timer in the while loop. When the timer hits the target, set a new PWM duty cycle, and add the next interval to your target time. This will work fine, until you need to start doing other things in the background loop.
You could set timer0's count to 0xFFFF-interval, and set it to interrupt on rollover. In the ISR, set the new PWM duty cycle, and reset timer0 count to the next interval.
One common way of controlling timing in embedded processes looks like this:
int flag=0;
void main()
{
setup_interrupt(); //schedule interrupt for desired time.
while (1)
{
if (flag)
{
update_something();
flag = 0;
}
}
Where does flag get set? In the interrupt handler:
void InterruptHandler()
{
flag = 1;
acknowledge_interupt_reg = 0;
}
You've got all the pieces in your example, you just need to put them together in the right places. In your case, update_something() would update the PWM. The logic would look like: "If it's on, turn it off; else turn it on. Update the tone (duty cycle) if desired"
There should be no need for additional delays or pauses in the main while loop. The goal is that it just runs over and over again, waiting for something to do. If the program needs to do something else at a different rate, you can add another flag, which is triggered completely independently, and the timing of the two tasks won't interfere with each other.
EDIT:
I'm now confused about what you are trying to accomplish. Do you want a series of pulses of the same tone (on-off-on-off)? Or do you want a series of different notes without pauses (do-re-me-fa-...)? I had been assuming the latter, but now I'm not sure.
After seeing your updated code, I'm not sure exactly how your system is configured, so I'm just going to ask some questions I hope are helpful.
Is the PWM part working? Do you get the initial tone? I'm assuming yes.
Does your hardware have some sort of clock pulse hooked up to the RA4/T0CKI pin? If not, you need T0 to be clock mode, not counter mode.
Is the interrupt being called? You are setting INT0IE, which enables the external interrupt, not the timer interrupt
What interval do you want between tone updates? Right now, you are getting 0xFFFF / (clock_freq/8) You need to set the TMR0H/L registers if you want something different.
What's on LATD7? and why are you clearing it? Are you saying it enables PWM output?
Why the call to Delay()? The timer itself should be providing the needed delay. There seems to be a disconnect about how to do timing. I'll expand my other answer
Where are you trying to change the PWM frequency? Don't you need to write to PR2? You will need to give it a different value for every different tone.
"Halting build on first failure as requested."
This just says you have some syntax error, without showing us the error report, we can't really help.
In Windows you can use the Beep function in kernel32:
[DllImport("kernel32.dll")]
private static extern bool Beep(int frequency, int duration);