Comments on: Momentary Button as On/Off Toggle using 555

By: SiliconFarmer

SiliconFarmer — Fri, 23 Jul 2010 19:16:00 +0000

Gumby,
Disconnect pin 4 from +5V. Put a 10K resistor from pin 4 to +5V and a 0.1uF capacitor from pin 4 to GND. That will give the circuit a short reset pulse when power is applied.

By: gumbydammit

gumbydammit — Fri, 16 Jul 2010 13:17:16 +0000

I was wondering, do you know of a way to make sure the circuit is always defaulting to “Off” when you power it up? I have the circuit working, but when I initially turn on the power supply I get the LED on sometimes and off sometimes, even though I have been making sure the circuit is in the off position when I power it down. I’d like this as a safety feature, but I lack the insight into that problem. Thanks in advance for any information and thanks for posting this. As a newbie I really needed to see the circuit in another form besides the schematic to make heads or tails out of it.

By: shanemag85

shanemag85 — Sat, 12 Jun 2010 11:13:30 +0000

now ive managed to get this working however i cant seem to get this to pulse aswell, is this possible?
Basically i want this so when the tactile switch is pushed the led will flash rather than stay on.
cant seem to get it to work

By: Wiley Wiggins

Wiley Wiggins — Fri, 19 Feb 2010 18:42:41 +0000

Yay! You rule! I’m going to start cranking these out after next month. Right now I am up to my eyeballs in VDMX (http://vidvox.com). By the way, if any of the geniuses on this blog can work out a way to have a MaxM change to a random color every time it senses a whack with an accelerometer (all on an arduino), I will pay you for your design! I want to have a kickdrum light up a different color every time it is hit.

By: todbot

todbot — Thu, 18 Feb 2010 21:55:10 +0000

Jeez you guys, it’s like you want correct schematics and reasonable pictures of the circuits. ;-)

I updated the schematic and included an overhead view.

By: Wiley Wiggins

Wiley Wiggins — Wed, 17 Feb 2010 20:20:40 +0000

I would love to cheat and get a clearer top-down photo of your proto-board by the way.

I guess for my finished jackets i’m going to try to build this on as small a piece of breadboard as I can, and then maybe seal it up in a blob of shapelock or something. I think there’s a lilypad protoboard that is big enough to accommodate the circuit, but I’m not sure.

By: Wiley Wiggins

Wiley Wiggins — Wed, 17 Feb 2010 20:18:13 +0000

Oh good. I thought I was just not building it correctly. (I am a novice at trying to put stuff together from a standard schematic and I’m spoiled by getting to use so many premade pcb’s with component maps.)

By: Calvin W

Calvin W — Mon, 15 Feb 2010 20:49:01 +0000

The circuit doesn’t work. I just tried building it from the schematic provided. I will now try the one left by underwood.

By: todbot

todbot — Mon, 08 Feb 2010 18:05:38 +0000

Underwood & Tim, I think you’re both correct: the schematic I drew above has an error. I could have sworn I wired it up exactly as the schematic I drew. Once I get back to my lab I’ll take a look at how I really have it wired up. :) For now, yes assume the bowden circuit is more correct one.

By: Tim

Tim — Mon, 08 Feb 2010 17:38:39 +0000

Looking at the photo, it appears that capacitor C1 is actually connected to R3 and not to the blue wire going to IC1 pin 2. So the proto-board is correct, but it didn’t get properly transcribed to the schematic.

By: Tim

Tim — Mon, 08 Feb 2010 17:27:35 +0000

I think the schematic may have an error. The referenced site shows capacitor C1 on the other side of the switch, connected to R3. I haven’t built the circuit, but intuitively the Bowden circuit seems correct – when the button is pushed, the capacitor will override the R1/R2 divider and momentarily pull the trigger pin high or low. As shown here, the 100K isn’t going to move the trigger voltage enough to get the trigger out of the hysteresis zone.

By: underwood

underwood — Wed, 03 Feb 2010 20:15:04 +0000

The circuit has an error and doesn’t work. The 1uF capacitor has to be tied to the 100k resistor. Look here: http://www.bowdenshobbycircuits.info/page9.htm#555-T.gif

By: Andrew

Andrew — Wed, 03 Feb 2010 17:25:04 +0000

Aha. Thanks for clearing that up.

By: todbot

todbot — Wed, 03 Feb 2010 17:04:00 +0000

Ivo, a BC547 transistor should work fine instead of the 2N3904 I use.

Andrew, yes you are correct that 555 chips have high drive capability. This makes them great for driving multiple LEDs usually.

In this case though, that can’t be done because the OUT pin is being fed back into input section of the circuit. The load from an LED connected directly to OUT screws up the input section, most notably not allowing the capacitor to charge up correctly. The transistor then is acting more like a buffer for the signal than an amplifier.

By: Andrew

Andrew — Wed, 03 Feb 2010 16:25:10 +0000

I have a 555 manufactured by Fairchild, and according to the datasheet, it can source, on its own, 200mA. I understand 555s are generally known for this relatively high capacity. Doesn’t that make this transistor redundant? One would have to be careful, of course, to make sure that their specific 555 has this capability, but most 555s, I belive, should be able to manage 60mA on their own. Please let me know if I’m mistaken, or if I’ve misunderstood.