#231: Circuit Fun: Stairstep generator using 555 and op amps

Here's an overview and demonstration of an interesting stairstep generator circuit that uses a 555 timer, a pair of op amps and a handful of transistors, diodes and passive components. It is a tutorial of different types of astable pulse generator / oscillator circuits and an interesting pulse integator / accumulator circuit. Thanks to one of my astute viewers (+11zekim), we now know that this integrator circuit is known as a Deboo Integrator.

My friend Pete K2LCN showed this circuit to me in a video he sent to me:
I modified the circuit to operate on a single supply using rail-to-rail op amps.

A link to the schematic that I used in this video can be found here:

Dino, KL0S put together an EXCELLENT set of annotations to the schematic - well worth a look. Here:

[vadble]

Alan Wolke, you are amazing person! ... Iam now 45yo ... but watching your videos is fulfilling my dreams about electronics from my childhood. Finally I found your lectures!

[BM-jycb]

I love the style of your videos - it's almost a cliché, but it really is like having a great teacher sit next to you and explain stuff. Thank you.

[rodrigocastro]

This video is still relevant in oct '23. I found some regular opamps in one of my bins, so I ordered the required r2r opamps and I will be building this circuit soon, just for fun and education.

[Georgy-]

Bravo! In all the time I've been following YT, I've only found two such excellent educators. You and DiodeGoneWild.

[jasoneyes]

The way you explain these circuits is engaging even for a novice like me. Using the scope as a demonsration is icing on the cake. Thanks!

[fluiddynamicist]

If the school teachers are as motivated and interesting as you are, we would have an army of young radio/electronics enthusiasts. Well done Alan! Good on ya mate!!!

[ottoomen]

Thanks so much. It's my new years resolution to build and describe 20 circuits. I may give the stairstep generator a shot!

[PelDaddy]

Great little tutorial on this interesting circuit. It's a very visual circuit on the scope as well; so that makes it more educational to visualize what is happening. Thanks for all your great vids.

[SeAfasia]

Nice circuit analysis Alan.
Thanks for your time to build it on breadboard...

[FFcossag]

What a refreshing video, to see an oscillator in this day and age that's not some super integrated proprietary PLL kind of deal or a microcontroller running one line of code is just very pleasant.

[robinharris]

Impatient to try this but waiting for rail to rail op amps to arrive...tried LM324. Got the relaxation oscillator running and adjusted pulse timings. Then the 555 pulse generator and added the reset. More adjustment to get about 12 steps between resets. Then added the pulse integrator but results were not as expected. Reset was not taking the integrator capacitor to ground. Eventually figured out that the 8k2 base resistor needed to be reduced to turn on a 2N3904 sufficiently to get down to ground during a reset. Guess this is a consequence of not using a rail to rail op amp. More adjustment of the base drive and finally an output close to yours. Not quite as square steps but close.

Spent a few hours working on this circuit because it looked fascinating and have learnt lots about basic electronics. There is no substitute for doing - great that your videos are, there is even more to be gained by building and modifying. Been great fun and learning.

[andymouse]

This is a great reason to get the breadboard out...cheers

[SeanBZA]

A little something for the first oscillator is you can use a linear pot and 2 diodes in the feedback network so you can have a near constant frequency ( roughly, you will have to vary C to get different frequencies) but where the duty cycle is variable over a very wide range, from around 5% to 95% as you turn the knob.

Can be used with the whole circuit to sample the output to get a specific step using a differentiator driving a sample gate ( 4066 switch). But I can see a use for an analogue staircase generator where you can select the number of steps easily just by using RC delays.

[dalekmoore]

I will give that a go ! This has got to be one of those few times when i wanted a circuit that does more with simple parts and better than i could of expected ...all the links very very helpful thank you !

[ohmslaw]

Such an amazing circuit.. ties in a lot of concepts together.. great for learning

[MrBanzoid]

That's a pretty elegant circuit, thanks.

[rene-jeanmercier]

Hi Alan, It reminds me of the basis of a transistor curse tracer on an oscilloscope of the 70's, when at school. It could be a "fun circuit" to see you build :-). Your videos are greatly instructive. Thank you for share so much knowledge with us. Regards, RJM.

[SouthShoreSonics]

Great video. This works really well with swapping out the 555s and op amp with 15ms trigger clocks for CV generation for electronic music gear.

[DavePKW]

This was just plain fun. Well done as always. Thanks a lot Alan.

[zekim]

Neat circuit! BTW that output stage is called a Deboo integrator, one of an interesting class based on Howland current sources. It's great for single-supply as it's non-inverting, unlike conventional Miller integrators.