need a tiny circuit

i am new to circuits. i need a circuit which is ON for 45 sec and OFF for 2 sec. i don't want to do it with arduino board i need it small like with smd components. plz help me.

by bharath875
May 25, 2021

You could use a ATtiny12, as example. It is a small 8 pins MCU compatible with Arduino. I never used it, but it seems to be a matter to "just" download the compiled program in it, and it is running. Well, you may have to add a capacitor here and there, but that is an avenuw for a small footpring. There are also "wearable" ESP32, another familly of MCU, often programmed in Python.

A solution based on a capacitor alone? consider R C = 45, even with R = 100k, you need C in the 450 microFarad ! That is not tiny. (And the circuit period may be proportionnal to more than just one time RC, requiring even greater than 450 uF).

Otherwise, it may be based around a CD4017BE, or two, and a crystal, no huge caps.

Still, if the footprint is critical and if you are not ready to move to surface mount technology, a tiny MCU seems the way to go, imho, given the 45 second.

by vanderghast
May 25, 2021

Here a preliminary sketch with a theoritical binary counter. See the description in the supplied link for more details.

by vanderghast
May 27, 2021

My mistake, the description does not appear. Assumption: the clock signal is at 32 768 Hz, that is, it counts from 0 to 32 768 in one second.

So, after 2 seconds, bit b16 is raised to a level high for the first time, which is an assumed voltage high enough to turn on the NMOS M1. That, in turn, switches the LED on.

Two seconds later, b16 turns back to zero (b17 turns to 1), that would turn off M1 if it was not for the diode D1 which "latches" the gate of M1 to be seen as a capacitor. So, even if b16 is at 0 volt, D1 forbid the gate of M1 to discharge and so, M1 stays on, and so the LED stays on.

At about 45 seconds after the LED turned on, the two output bits of the counter, tied to the AND gate AND1, turn on for the first time. That would reset the counter to zero (orange wire), but that also turns on NMOS M2 which then allors the gate of M1 to discharge. So, M1 turns off.

At the next clock edge, the output of AND1 becomes 0, which discharge the gate of M2, turning M2 off, and we restart the sequence, properly.

Note that we could use a 3 inputs AND gate for more precision, if required, using b20, b18 and b17 for input, as example.

The binary counter is theoritical. Could use one IC or multiple IC, in cascade, to get the proper number of bits for the output. Here, 47 second period, at 32768 count per second, implies to be able to write the binary representation of 1 550 096, which requires 21 bits.

WARNING: the circuit has not been tested. Be sure that M1 is turned on with an output of the binary counter, given the presence of diode D1.

by vanderghast
May 27, 2021

thanks a lot for ur time and information. i am a CSE student so i've understood only about that ATtiny 12.

by bharath875
May 28, 2021
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2 Answers

Answer by Foxx

How Small?

+1 vote
by Foxx
May 27, 2021

like 20x30 mm, is it possible

by bharath875
May 28, 2021

here it is for powering a device. The load is 5v and around 100 mA.

by bharath875
May 28, 2021

Use an LM555, or if micropower is enough, use the LMC555.

by Pebri
June 05, 2021
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Answer by jstockma

Use the timer/counter on and AVR Tiny Microcontroller, you could set up its control registers or use a "canned" function from a library.

+1 vote
by jstockma
May 30, 2021
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