ATTiny2313 AnalogRead Not Working for LDR and PIR Sensor Project—Why?

243 12

#1 21671942 16 Jul 2014 04:03

Jay Reyes Jay Reyes

Anonymous

Post #1
21671942 16 Jul 2014 04:03

im creating a miniature project that works at night , if the LDR detects less than 500 analog input(not sure what this number is. but if i run serial monitor, these are the readings), it will pass through the PIR/Body Sensor, then when the sensor detects movement the LED and Buzzer will turn HIGH. this program works fine in the arduino itself, but when i upload it to the ATTiny2313, it seems that the analog inputs or AnalogRead wont work i guess. When i connect the IC on the 5V power supply, it will automatically turn the LED and the BUZZER, why? my codes attached bellow. Also, i follow the instruction on how to use ATTiny2313 correctly.
See reference:. http://www.instructables.com/id/How-to-Program-ATtiny2313-Current-and-Updated/.

i also connect the pins correctly with analog and digital inputs and outputs. here the link:
http://www.element14.com/community/servlet/Ji...mage/2-50246-76876/ATtiny2313-PIN+MAPPING.PNG

sorry for bad english.
please help me.

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#2 21671943 16 Jul 2014 23:43

Neil Mula Neil Mula

Anonymous

Post #2
21671943 16 Jul 2014 23:43

Hi Jay,

Can you post the complete circuit design here.

I think you have a problem with the sense Pin connection.

If your LED and Buzzer become active, this means your LDR is shorted or something.

Try to check the LDR and some of the connections.

God Bless.

Best,
Neil
#3 21671944 17 Jul 2014 00:35

jay reyes jay reyes

Anonymous

Post #3
21671944 17 Jul 2014 00:35

This is my Circuit Connections. assume that the PIC is ATTiny2313.
any ideas whats wrong with my work then??
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#4 21671945 17 Jul 2014 02:35

Neil Mula Neil Mula

Anonymous

Post #4
21671945 17 Jul 2014 02:35

>Have you tried removing the PIR sensor from the circuit?

>If the same will happen
-try to connect the PIR sensor with the other I/O pins

>If the same will happen
-try to adjust the value assign with the LDR Lower or Higher than 500

or try this
//Define properly the pins
int motionPin = 0; //for PIR
int lightPin = 1; //for LDR
int ledPin = 9; //for LED
int speakerPin = 5; //for LED

//Set the distance variables for motion detection
int lastDist = 0;
int currentDist = 0;

//Set a threshold
int thresh = 150;

void setup()
{
pinMode(ledPin, OUTPUT);
pinMode(speakerPin, OUTPUT);
}

void loop()

{
int lightVal = analogRead(lightPin);
currentDist = analogRead(motionPin);

if(currentDist > lastDist + thresh || currentDist < lastDist - thresh && lightVal < 500)
{
digitalWrite(ledPin, HIGH);
digitalWrite(speakerPin, HIGH);
delay(1000);
}
else
{
digitalWrite(ledPin, LOW);
pinMode(speakerPin, LOW);
}

lastDist = currentDist;
}

Just follow the assigned pinning.

I hope it helps.

Good Luck.

Best,
Neil
#5 21671946 17 Jul 2014 03:17

jay reyes jay reyes

Anonymous

Post #5
21671946 17 Jul 2014 03:17

ok tnx ill try this . tnx alot.. for helping
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#6 21671947 17 Jul 2014 03:41

jay reyes jay reyes

Anonymous

Post #6
21671947 17 Jul 2014 03:41

Hi Neil

>I tried to remove the PIR sensor. same things happen.
>i tried to connect it from other I/O, still same things happen.
>i tried to change the value of my resistor 220 ohms. still same things..

>i tried your code. and i got these errors:

sketch_jul16a:25: error: stray '' in program
sketch_jul16a.ino: In function 'void loop()':
sketch_jul16a:25: error: expected `)' before 'u2013'
#7 21671948 17 Jul 2014 17:56

Neil Mula Neil Mula

Anonymous

Post #7
21671948 17 Jul 2014 17:56

Hi Jay,

I just uploaded the .ino file

Try it again Jay.

The codes are affected by the format of this comment.

Best,
Neil
#8 21671949 18 Jul 2014 05:30

jay reyes jay reyes

Anonymous

Post #8
21671949 18 Jul 2014 05:30

Hi Neil,

i tried your attached .ino file. it didnt work at all, i even check every single pins, i even change the ATTiny2313 a new 1. but it didnt work.
#9 21671950 18 Jul 2014 05:40

jay reyes jay reyes

Anonymous

Post #9
21671950 18 Jul 2014 05:40

i wonder if my components affects about the problem.. i have 30kOhms right next to LDR..
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#10 21671951 18 Jul 2014 18:27

Neil Mula Neil Mula

Anonymous

Post #10
21671951 18 Jul 2014 18:27

Hi Jay,

From your Fritzing Diagram

Aside the Dev kit Uno.

This PICAXE-20M, is this a raw AVR?

Best,
Neil
#11 21671952 18 Jul 2014 23:06

jay reyes jay reyes

Anonymous

Post #11
21671952 18 Jul 2014 23:06

ihi Neil,

i didnt used PICAXE-20M, i actually used ATTiny2313, because i cant find the ATTINY at the Fritzing software..

> do really ATTINY supported analog signals? thats my last question./.

Jay.
#12 21671953 19 Jul 2014 02:24

Neil Mula Neil Mula

Anonymous

Post #12
21671953 19 Jul 2014 02:24

Hi Jay,

The ATTiny2313 AVR does not have ADC.

Therefore the analog pins does not work.

But you can add ADC component to have some analog pins since SPI is available on the ATTiny2313.

However, this will surely affect your design.
-the cost
-the size

Comparing this to atmega that have built in ADC.
-having atmega is much easier.
-the cost between those options basically is not that far.

And I think most of the PIR sensors only requires digital I/O pin.

I think your PIR sensor is requires only digital I/O.
same with this one -> http://playground.arduino.cc/Code/PIRsense

And this "the LDR detects less than 500 analog input(not sure what this number is. but if i run serial monitor, these are the readings)"
-It is a value of voltage in digital bit ( sample 5V using 8 bit 2^8 =256bits therefore 5V=255 starts with 0)

I hope it helps.

God Bless.

Best,
Neil
#13 21671954 21 Jul 2014 00:21

jay reyes jay reyes

Anonymous

Post #13
21671954 21 Jul 2014 00:21

Hi Neil,

ok,, tnx for the advice. and help..

My gratitude.
Jay
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Topic summary

✨ The discussion addresses an issue with using analogRead on an ATTiny2313 microcontroller for a night-activated project involving an LDR and a PIR sensor. The project works correctly on an Arduino but fails on the ATTiny2313, where analog inputs do not function as expected, causing the LED and buzzer to activate immediately upon powering the IC. Troubleshooting steps included verifying circuit connections, testing with and without the PIR sensor, changing resistor values, and trying alternative code. The key insight revealed is that the ATTiny2313 lacks a built-in Analog-to-Digital Converter (ADC), so it cannot perform analogRead operations directly. This limitation explains why analog input readings fail on the ATTiny2313. Suggested solutions include adding an external ADC via SPI, switching to a microcontroller with built-in ADC like an ATmega, or using the PIR sensor as a digital input since it typically outputs digital signals. The LDR readings referenced (values around 500) correspond to digital bit values from ADC conversion on Arduino platforms, which the ATTiny2313 cannot replicate natively.

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ATTiny2313 AnalogRead Not Working for LDR and PIR Sensor Project—Why?

FAQ

TL;DR: Your ATtiny2313 has 0 ADC channels, so analogRead won’t work. “The ATTiny2313 AVR does not have ADC.” Use a digital PIR and either add an SPI ADC or switch MCUs. [Elektroda, Neil Mula, post #21671953]

Why it matters: This FAQ helps makers debug night‑triggered LDR/PIR builds that fail after moving from Arduino boards to an ATtiny2313.

Quick Facts

ATtiny2313: built‑in ADC count = 0; SPI is available for external ADCs. [Elektroda, Neil Mula, post #21671953]
Typical PIR modules expose a digital OUT pin usable on simple I/O. [Elektroda, Neil Mula, post #21671953]
analogRead requires an ADC; without one, thresholds like “<500” cannot be evaluated. [Elektroda, Neil Mula, post #21671953]
Switching to an ATmega with onboard ADC simplifies cost/size tradeoffs versus adding an external ADC. [Elektroda, Neil Mula, post #21671953]
Symptom: LED/buzzer turning on at power‑up indicates the analog path isn’t valid on ATtiny2313. [Elektroda, Jay Reyes, post #21671942]

Why doesn’t analogRead work on my ATtiny2313 LDR/PIR project?

Because ATtiny2313 has no ADC. Without an analog‑to‑digital converter, analogRead cannot sample the LDR voltage, so your threshold logic never evaluates correctly. As Neil put it, “The ATTiny2313 AVR does not have ADC.” Use a digital PIR and add an external SPI ADC or change MCU. [Elektroda, Neil Mula, post #21671953]

Does a PIR sensor need an analog input here?

No. Many hobby PIR modules provide a single digital OUT pin that goes HIGH on motion. Wire it to a digital input and skip analogRead entirely on ATtiny2313. This matches the Arduino Playground‑style PIR modules Neil referenced. [Elektroda, Neil Mula, post #21671953]

Why do my LED and buzzer turn on immediately when I power the ATtiny2313?

Your sketch expects a valid analog threshold, but the chip lacks ADC. At power‑up, your code likely treats the unmeasurable LDR path as a trigger, so the LED and buzzer go HIGH right away. That exact symptom was reported in this thread. [Elektroda, Jay Reyes, post #21671942]

Can I add ADC capability to the ATtiny2313?

Yes. Use an external ADC (e.g., SPI‑interfaced). The ATtiny2313 exposes SPI, so you can read the LDR via that converter and keep your small MCU. Expect added cost and board area compared with picking a chip that already includes ADC. [Elektroda, Neil Mula, post #21671953]

Should I switch to an ATmega instead of bolting on an external ADC?

Often yes. An ATmega with onboard ADC simplifies wiring and code and keeps costs near an external‑ADC solution. Neil noted the cost gap is small, and integration is easier with built‑in ADC channels. [Elektroda, Neil Mula, post #21671953]

What does “less than 500” mean in my LDR readings?

That number is an ADC count from the board where your code originally worked. Neil explained it as digital bits representing voltage (e.g., 0–255 style). The ATtiny2313 cannot produce that number without an ADC, so the comparison fails. [Elektroda, Neil Mula, post #21671953]

How do I quickly isolate the fault before redesigning?

Try this 3‑step check: 1. Remove the PIR module and test. 2. Move the PIR to another I/O pin and retest. 3. Adjust the LDR threshold in code and observe behavior. Neil suggested these steps to pinpoint the failing path. [Elektroda, Neil Mula, post #21671945]

I copied code from a comment and got compile errors—what happened?

Forum formatting can inject stray Unicode characters (like en‑dashes), breaking Arduino IDE compilation. Use the attached .ino or retype the lines to remove hidden characters. Jay reported stray character errors traced to formatting. [Elektroda, jay reyes, post #21671947]

My PIR is removed, but the issue persists—what next?

That confirms the PIR isn’t the root cause. The failure stems from relying on analogRead on a microcontroller without ADC. Rework the design: use a digital PIR and either add an SPI ADC for the LDR or switch MCUs. [Elektroda, jay reyes, post #21671947]

Does my 30 kΩ resistor next to the LDR affect the problem?

Component values set the light threshold, but the core issue is lack of ADC on ATtiny2313. You can optimize the divider later; first restore a valid analog measurement path via an external ADC or a different MCU. [Elektroda, jay reyes, post #21671950]

What is an ADC, in plain language?

An ADC (analog‑to‑digital converter) turns voltages from parts like LDRs into numeric counts for code comparisons. Without one, analogRead comparisons such as “<500” cannot run on ATtiny2313. “The ATTiny2313 AVR does not have ADC.” [Elektroda, Neil Mula, post #21671953]

How can I port my working Arduino prototype to ATtiny2313 cleanly?

Keep the PIR on a digital pin. For the LDR path, add an SPI ADC and map its reading to your threshold. Your Arduino‑side success shows the logic is fine; you just need equivalent ADC hardware on ATtiny2313. [Elektroda, Jay Reyes, post #21671942]