Skip to main content
shopping_basket Basket 0

Getting to Grips with 555 Timer Basics

Trainee Electronics Engineer, currently studying towards my degree in Electronic Engineering at the University of Hudderfsield. Completed my HND in Electrical & Electronic Engineering from Bradford College 2017. Love to try new things and build interesting projects!


[Comment was deleted]

May 13, 2016 07:41

Thank you to everyone for their feedback and mentioning the duplicate image, this has now been replaced with the toy organ schematic. The other comments are very helpful for someone who is still has a lot to learn - all of these comments will be taken into consideration if I design my own 555 timer based circuit and in this post I was strictly following the examples from the Engineers Mini Notebook..

May 11, 2016 08:55

Nothing very new here from memory I first came across and used the NE555 back around 1972. It has been incorporated in dozens of our products ever since,and still is used.

0 Votes

May 11, 2016 08:45

My first OMG you can't do that is simply that you cannot simply leave an IC pin open and then touch it! Has no-one heard of STATIC? Yes the circuit will work but how many times before the static voltage on the user degrades the IC input such that the circuit no longer works? No professional engineer, or anyone professing to be or be becoming an engineer, would do this. That input needs protection. The simplest is probably two diodes (1N4148?) from the input pin, one to the +ve rail, the other to GND, both non-conducting with the input pin is 'mid' rail and a series resistor (10K?) to the touch pad.
Bipolar vs CMOS. Yes the CMOS is much less robust particularly to static discharges from fingers but the bipolar is sensitive is too though the bipolar will probably keep working longer. Do they behave differently? Not particularly so but I will always use the CMOS version: the biploar tends to crowbar the supply - hence JMW1937's 220uF decoupling cap (use 10uF up for the CMOS) - and cause spikes and noise on the supply rail that can upset other circuitry.
If you want a symmetrical output that is as near as damn-it 50-50 MS then connect pins 2&6 to your timing cap and timing resistor. Connect the other end of the timing cap to the output pin 3. Leave pin 7 open. There is only one timing resistor now and the cap charges and discharges symmetrically through it as the output switches between GND and rail.

0 Votes

May 10, 2016 22:52

Hey Don,

Click on the link that Chelsea provided to "Engineers Mini Notebook – 555 timer IC circuits" by Forrest M Mimm, and you can find the circuit in there.


0 Votes

May 10, 2016 16:30

Thanks for the link jwzumwalt, but it can't be the same circuit as the one described uses different values of capacitor, as shown in the close-up photos.

0 Votes

May 10, 2016 15:24


0 Votes

May 10, 2016 15:21

The circuit can be found by going to Google Images and searching for "555 toy organ" :)

or see this ... -a-555-IC/


0 Votes

May 10, 2016 09:52

The toy organ project circuit diagram seems to have got lost and instead the touch activated circuit is shown twice.
I would be interested to see the real toy organ circuit as I can't see how they are combining the trigger with the different capacitors.
Could you check and hopefully correct the diagrams on this page.

Don Stewart.

0 Votes

May 10, 2016 09:26

The 555 does NOT like disturbances on its supply rails. If you aren't using a very stable lab power supply, **connected by short wires**, you need a 220 uF capacitor across the supply near the 555.

The bipolar and CMOS version of the 555 behave differently. The CMOS versions are less robust than the bipolar, but produce symmetrical square waves in astable mode more simply.

0 Votes

Related Content

DesignSpark Electrical Logolinkedin