555 timer circuit

MusicMan11712 · Posted: Sat Nov 06, 2010 6:23 pm Post subject: 555 timer circuit

While looking through a box of old files on music, I found my 555 timer circuit from a few decades ago. The actual object can be seen here (well, most of it): http://electro-music.com/forum/post-278450.html&highlight=#278450

So, here's the diagram. I may try to rebuild it to see if it still works as I know some of the wires fell off over the years.

MusicMan11712 · Posted: Fri Jan 07, 2011 5:43 pm Post subject:

I just found another sketch of my ancient 555 timer sound device showing ideas I had for modifying it.

JovianPyx · Posted: Sun Jan 09, 2011 12:43 pm Post subject:

When do we get to hear what it does? Smile

blue hell · Posted: Sun Jan 09, 2011 12:49 pm Post subject:

JovianPyx · Posted: Sun Jan 09, 2011 1:06 pm Post subject:

hmm. I was a tad late... He's offline...

blue hell · Posted: Sun Jan 09, 2011 1:13 pm Post subject:

It'll come back I guess

phobos · Posted: Mon Jan 10, 2011 7:23 am Post subject: Testing Dr. Steve's 555 Circuit

Thanks Dr. Steve for posting these schematics Wink

I've been experimenting with this circuit and will post my
findings and progressions in the next couple of posts:

The first thing I did was redraw the schematic so I could
understand a bit better what's actually going on.

DrSteve555 - Org .gif

Description:

Original 555 circuit by Dr. Steve, redrawn by PHOBoS

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phobos · Last edited by phobos on Mon Jan 10, 2011 8:31 am; edited 1 time in total

I noticed a couple of things from the original schematic:
pin 8 of the second 555 timer wasn't connected to V+
(I assumed this was just an error in the schematic)

Pin 3 of the first 555 timer goes to pin 5 of the second timer,
which makes sense, but it's also connected to pin 3
of the second 555 timer. Since the outputs of the 555 both
oscillate between V+ and V-, this would short the powerlines.

I know Dr. Steve made this circuit by experimenting, so I decided
to just give it a try anyway. It did do something but the second
555 got very hot. So I decided to change this part in the schematic
to something that seems to make a bit more sense.

I also looked up the 142n9 transistors, and found out they are NPN
instead of PNP so I redraw those aswell.

this resulted in the following schematic:

DrSteve555 - Rev1 .gif

Description:

Dr. Steve's 555 Circuit modified by PHOBoS

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JovianPyx · Posted: Mon Jan 10, 2011 7:47 am Post subject:

I noticed that too - about the pin 3 to pin 3 connection... Also, it's not clear to me where power + is connected. Is it on the upper "bus" that connects the pins 8?

I've seen circuits like this before, where outputs are connected together to get a kind of ring modulator sound. But as you point out, with pin 3 of one connected to pin 3 of the other, it's possible for + to connect to - through the output transistors. Some circuits like this have recommendations to use batteries that are partially drained so as not to provide enough current to allow damage to the ICs. A dubious recommendation at best I think. Low voltage can help too. Or one could simply put a resistor between the + rail and pin 8 of each chip to force limiting the current to some acceptable level. This would prevent chip self destruct and/or overheating.

I see that in your second schmatic (PHOBoS) you have eliminated the right 555 pin 3 connection to the other pin 3 - yet in both of Steve's drawings, they are connected together or can be through the switches. This connection would also appear to provide self modulation of the right 555 timer.

It might be interesting to use a high input impedance opamp to get a signal from the timing capacitor(s).

phobos · Dr Steve's 555 Circuit - Demo 1 (Jan 10, 2011).mp3

phobos

Last week Dr Steve was kind enough to turn on his webcam to retrace
the connections on his breadboard. unfortunately a lot of the componenta
are missing but we did manage to retrace some connections of the transistors.
There were a lot of unconnected wires and some had probably been connected
to Steve's potbox.

Posted below is the schematic that I got from that:
As you can see this also solves the question about the 2 555 outputs being
connected together. I might recreate something using this as a starting point
but for now I'll continue with my last schematic.

DrSteve555 - Bread.gif

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Dr. Steve's 555 Circuit, retraced form breadboard.

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phobos

Here's a ±10 minute excerpt from my Solar Control Test with the circuit
triggered by my Treequencer. I placed 2 LDRs in series with the frequency
pots so that the frequencies changed over time while the sun was slowly
disappearing behind a building. sunny

And the added delay creates a nice phasing effect.

(Thanks to tjookum for the tip of using heat shrink tubing on the LDRs !)

Dr Steve's 555 Circuit - Solar Control Test (Jan 10, 2011).mp3

Description:

Testing Dr. Steve's 555 Circuit with 2 LDRs changing the frequencies
controlled by the sun slowly disappearing behind a building.

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phobos

Next test: CV control.
Using a vactrol (LDR-LED combo) in series with the second 555 frequency
pot I was able to use a sequencer to change the frequencies.

I also made some further adjustments to the circuit.
- A couple of different caps to choose a different decay time.
(this was also suggested in Dr. Steve's second schematic).
- An extra cap to choose a higher frequency for the first 555.
- Resistors in series with the frequency pots so I can use the full range.
- A LED and an extra resistor to get rid of the soft noise when the circuit is
not being triggered. (This LED also functions as a very nice indicator)
- A simple trigger circuit connected parallel to the Trigger switch.
(before I just hooked up the Treequencer instead of the switch)

Posted below is the schematic and a recording done by using a sequencer
for both CV control and triggering the circuit. (and delay for the nice phasing)
If you listen closely you might notice that the circuit produces some weird
background noises too.

Dr Steve's 555 Circuit - Pulsing Vactrol Drone (Jan 13, 2011).mp3

Description:

Using a sequencer controlled Vactrol to change the frequency of the second 555.
Circuit is triggered by the CLK of the sequencer

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5.94 MB

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DrSteve555 - Rev3.gif

Description:

Dr. Steve's 555 Ciruit Heavily modified by PHOBoS (rev3)

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JovianPyx · Posted: Sat Jan 15, 2011 10:00 am Post subject:

The LED looks like it's drawn backwards...

phobos

JovianPyx · Posted: Sat Jan 15, 2011 10:31 am Post subject:

I figgered that would be the answer, but I had to make sure... very odd... That means the LED conducts only when pin 3 of the right 555 is at ground potential, so the + end of the circuit is somewhere else. I see two candidates, the trigger switch through the 2.2k through the base-collector diode (which might not be a good thing for the transisitor)

OR

possibly from + to the collector of left transistor through it's collector-base diode and then avalanching the emitter base junction of the right transistor (????)... Very odd indeed.

phobos · Posted: Sat Jan 15, 2011 11:41 am Post subject:

JovianPyx · Posted: Sat Jan 15, 2011 11:50 am Post subject:

The caps on the multi-switch might also be able to supply the + side of the circuit while they are charged. I'd bet the LED might change brightness when the cap value is changed.

Wonderful mental gymnastics, eh? Smile

phobos · Posted: Sat Jan 15, 2011 1:09 pm Post subject:

phobos

More CV controlled sounds.

Later that evening Tjookum joined me, excerpts from that jam session can
be found here. Basketball

Dr Steve's 555 Circuit - Hypnotropia (Jan 13, 2011).mp3

Description:

Using a sequencer controlled Vactrol to change the frequency of the second 555.
Circuit is triggered by the CLK of the sequencer

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14.68 MB

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MusicMan11712 · Posted: Mon Jan 17, 2011 7:05 am Post subject:

Thank you so much for breathing new life into my ancient experimental 555 circuit, PHOBos. Thanks also to JovianPyx for adding to the discussion of the design and redesign, and to TJookum for participating in the demos.

Now that I found four more of my ancient 555s and a whole bunch of other parts (including the transistors taken from an old Magnavox Odyssey*), perhaps I can build your version--or something close to it--without taking my museum piece apart!

Steve

*http://www.magnavox-odyssey.com/Manuals.htm has a couple of versions of the service manual as well as operating manuals.

Footnote:
I used a 9 volt battery which was probably not operating at full capacity most of the time.

phobos

-minus- · Joined: Oct 26, 2008 Posts: 787 Audio files: 13

MusicMan11712 · Posted: Tue Jan 18, 2011 6:29 pm Post subject:

LOL!!!!!!

I remember those little boards. They were fun to desolder!!!!

Either I found it in the trash or someone gave it to me as a non-working unit. I am guessing this was about 30 years ago or so. Back then, it was worthless.

Lemme see what other trash--errrr, I mean collector's items I have around here. I wonder what they are worth. Hmmmmmm. A Roland MT-32? A Casio CZ-3000? A Commodore 64? About 20 or so SCSI Cables?

Steve

-minus- · Joined: Oct 26, 2008 Posts: 787 Audio files: 13

I was going to comment but it turned into a rant and I hit the delete button! Laughing

Anyway, I'll forgive you for your transistor barbarianism. You were not to know... Besides, I sent a Jupiter 4 to the garbage dump in 1992 because the on/off button was broken Shocked