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Building The Astable Multivibrator Part 1

Building The Astable Multivibrator LED Flasher

This is the part where you get to build your circuit onto a solderless breadboard. If you follow the steps below carefully and make sure that you check to make sure everything is where it should be and in the correct way around then it should work for you.

Solderless breadboard ready to go
Start here with a nice shiny clean solderless breadboard.

Insert the connecting wires first
Cut some solid connecting wire to length and insert into the holes in the board as shown here. I used bare 0.7mm (1/32" or 0.0276") (21 AWG/22 SWG) tinned copper wire but you can use insulated wire of the same diameter. Cut to length and strip the insulation from both ends and it will work just the same.

Insert transistors the correct way
Transistors have 3 legs and come in different packages. Most general purpose bipolar junction transistors (BJT) will work in this circuit but you must make sure that you insert the leads in the correct positions. Make sure that the Emitter leads of both transistors are on the outside of the board, the Base leads next and the Collector leads innermost. You may have noticed that this circuit is a mirror image down the middle.

LEDs go in next
Insert the LEDs as shown in the picture. Notice that the larger internal metal electrode is the negative side of the LED and should be connected to the collector of the respective transistor.

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Comments (5)

Topic: How To Build An Astable Multivibrator Circuit Without Solder
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Amalia (US) says...
Can anyone tell me how to place 2 toy DC motors on the breadboard so that they intermittently go on and off like the LEDs? Or is this not possible? I want to use it to power a toy that zig zags. I'm going to try it anyway tonight but I would like help on where to connect the motors on the breadboard since I am a novice. Thank you.
19th August 2019 8:10pm
Richard says...
An excellent little circuit! Thanks. I shall be using this for a dummy alarm. Any ideas how long the nine volt battery will last (i.e how much current does the circuit consume)?
6th August 2015 3:56pm
Steve (UK) says...
Hi Richard,

As it stands the circuit consumes about 15mA and if the battery is alkaline with a capacity of 625mAh then it should last approximately 30 - 40 hours.

You can try increasing the values of the two collector resistors R1 and R4. Common high efficiency LEDs will still glow brightly with only 1mA so try replacing the 470 ohm resistors with 4.7k ohm. This theoretically should allow the battery to last for up to 600 hours.

6th August 2015 11:34pm
James says...
Wow, super cool... my first brush with electronics! I am curious, how can you change the rate of flashing? Also, how would you apply this circuit to producing a audible noise (sine wave)? Again, thanks so much!
23rd November 2014 8:59pm
Steve (UK) says...
Hi James, I'm so pleased that I've interested you in electronics. You are where I was 50 years ago. The flashing rate is controlled by the two pairs of resistor/capacitor R2/C1 and R3/C2. Increase the values of the two capacitors to slow the flashing rate. Decrease the values to increase the flash rate. You cannot use this circuit to produce a sine wave but you can make it produce audible signals. Signals become audible at around 5Hz to 16KHz. If you decrease the capacitor values so ... Read More
23rd November 2014 11:46pm

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