555 to drive a PASSIVE buzzer/speaker - Page 1
Forum section: electronics / projects

author: digik
author_rank: Regular Contributor
timestamp: April 25, 2021, 02:45:25 pm
content: Like the title says, I want to make a beep beep tone alarm using a 555 and less external components as possible, but all the schematics refers to an active buzzer, for example this one:http://www.circuitdiagram.org/images/buzzer-circuit-555.gifI want a beep-beep sound (NOT a continous one) but I only have a standard toy speaker. It's possible? can someone post a decent working schematic?

author: pqass
author_rank: Super Contributor
timestamp: April 25, 2021, 03:29:26 pm
content: Quote from: digik on April 25, 2021, 02:45:25 pmSimilar to (bottom of) this page:https://www.electronics-tutorials.ws/waveforms/555_oscillator.htmlBut instead of connecting IC1 pin 3 (output) to a 10K to IC2 pin 5 (control),connect IC1 pin 3 (output) to a 10K to base of an NPN transistor, emitter to ground, and then collector to IC2 pin 4 (reset) with pullup to V+. See attached simulator image below.Play with it here:http://www.falstad.com/circuit/circuitjs.html?ctz=CQAgjCAMB0l5BOJyWoSATAZmgFgOyQCsCGYAbOfkZFkSDQw5AwKYC0YYAUBfRgA4BILBhZ0MIsSHIhc0ZEXK1qYfGPy5uAJ0xCRRSYOHGoMgfG4B3PcNwVbc3MMg7HEx-dktyFuNwATTCUDIxCvTBAA1gAzAEMAVwAbABdrYNkI0wjXGwwQj1MPVwBjT2dHIjBJFhh4OAJMaEJyXCJ8LCpIAiwBfChYSB4yj2dxQwZqszAOYRwsBcWl5fo6ofSPKqN9LahuAHNQyclNwTNckQFcOQtL692L3vupzanXACUjoomMDGvauQsVbnaBEdIRUYOUwXLL6Qr6C6mb7bFzghxPY53PY2fC+LFXOZXbEyXAsUyEa7Q9K4kwhJRkkIXGlHZn5bzcT4Uxxc37-MykpgAmBgnGdTFch7UsVjEAdWSSw4SqYSs61andTGtIFvbhlLkypU1cCzETQZbmxY1QbDEksXAVLWYlgzdj9NbKBBDBYIAQYBAEcgLAZwHi6R0eR05EC+-w2SMOSMVVxhgURgXQ6NiVx8W1SFhc0Q+PYpTFYDX0kQa50Ddp0OCBxC0BBERnQZQLaqIEiQXFqdBgOBRWKJVJuXZl54nInO+oHBjKPPz8RitW6CumR0ZgeWGzrukLqkAe3A-Qcdr692D8AQuKU+TMkjUIhAABkAKIAMQAKgAdADOADyACqX4AAogdwx5gMIZ43JogrQBAZLgHMIDvAAkgA4gAEr+gEgeBX7cEAA

author: digik
author_rank: Regular Contributor
timestamp: April 25, 2021, 03:45:49 pm
content: thanks, the default output tone should be 300Hz, right?Why the simulator shows 2.126 Hz?just in case I need: what component should I change to achieve a lower frequency sound?

author: pqass
author_rank: Super Contributor
timestamp: April 25, 2021, 04:07:02 pm
content: Change either the TH capacitor to ground and/or resistors between V+ and DIS and TR. Lower = faster; 10x lower = 10x faster.With current values, the left 555 is 2.1Hz, right 555 is 500Hz.EDIT:It's hard to see the lower waveform frequency as per the screenshot.You have to disconnect the left 555 output temporarily and zoom into the upper waveform (by hovering the mouse over it and using control-scrollwheel-up until you see the lower waveform clearly) then the frequency on the lower waveform will be shown correctly.

author: digik
author_rank: Regular Contributor
timestamp: April 25, 2021, 04:13:04 pm
content: thank you again, of course you mean in the right one, since it will be connected to the speaker

author: Zero999
author_rank: Super Contributor
timestamp: April 25, 2021, 06:17:14 pm
content: The circuit can be simplified significantly and why not use the NE556, which contains two 555 timers? It will work out cheaper and save board space.https://tinyurl.com/yj34okrb

author: pqass
author_rank: Super Contributor
timestamp: April 25, 2021, 06:17:31 pm
content: See attached, a new version with fewer components.It utilizes the built-in discharge transistor as an open-collector output for a reset pin toggle (left 555) and a speaker amplifier (right 555).Although, you probably don't want to push more that 20mA through the transistor (can't find a documented Ic) so I limited the speaker with an in-series 220R.Current values give 2.25Hz (left 555) and 714Hz (right 555).Play with it here:http://www.falstad.com/circuit/circuitjs.html?ctz=CQAgjCAMB0l5BOJyWoSATAZmgFgOyQCsCGYAbOfkZFkSDQw5AwKYC0YYAUBfRgA4BILBhZ0MIsSHIhc0FCSwJytBALAZuAJzkUGuXHtlYBRluQHxuAd0xDj94YeGRbmIrNz7Bz-W7tfcHxZIIkobgBjJzlcYSCiTSgoWHhIAkxobCEESDBaDFx1LFkYOB5o8LjxIklEyRYwDmEcLDb2jo7zVJ47cPqYgbcAcxFahiT+wWSAkTM5KzmjIfdTZcnxlYAlMckw8YxCmbkWehZz6CJ3bxNxm5jZ+-29h0f9NblyIw-ZkOEwEIxAGldx-GJg4ERHaEIxBGGYI7nE5MJEwK52fAlCaSeErDFY6ogTGyFajXFJXHTc6g9LYmS4U5JNzReGE8kNcDNETQTq89oNHpReksFzCumNDj4TIYUhgIT4QRgXDkMiuQW6MEfMFEQzJARiWZfEX6I2xVy8cj0U2iFjwm0yFLwDD4BA0LgYWrK5WCfA6ImWcG0oKNNI02EOTwsYPuVTCHVGWOOQ2QOO67W65N+WSm+5uXTWzaqXbJQ5lNLl+BYP2RwZF8IsARZa76eMeEkZ9we9uwzxJ0EBuEB+v9lrzDQmeZuAAeckIUiwBkkoi84FkAGUAAoAUQAggBpLdbbgAe3ARn8C3wy0d8AQIU8HpLZ5EIAAMluAGIAFQAOgBnAB5ABVL8NxAk8RClC9cBKOobzgO9LRVM5MEgl8tgASQAcQACV-QCQLAr9uCAA

author: pqass
author_rank: Super Contributor
timestamp: April 25, 2021, 06:22:05 pm
content: Quote from: Zero999 on April 25, 2021, 06:17:14 pmTrue.But since the output on some 555's don't reach Vcc I wasn't sure direct attachment to the reset input would work.Yes, the diligent student should recognize that the circuit begs for a 556 but alas, falstad.com only has a 555 defined.

author: Zero999
author_rank: Super Contributor
timestamp: April 25, 2021, 06:29:26 pm
content: Quote from: pqass on April 25, 2021, 06:17:31 pmConnecting the 555 timer like that will work, but beware, the simulator is lying to you about the frequency and duty cycle, because the model doesn't take into account the asymmetry of the totem pole output stage, which as you said, doesn't reach VCC. That configuration is better suited to the ICM7555 timer, which has a CMOS output stageThe real waveform looks more like the post linked below.https://www.eevblog.com/forum/beginners/trying-to-understand-this-555-circuit-i-used-a-long-time-ago/msg3546398/#msg3546398Quote from: pqass on April 25, 2021, 06:22:05 pmIt should work. The data sheet specifies a maximum of 1.1V for the reset voltage.https://www.circuitbasics.com/wp-content/uploads/2015/01/555-Timer-Datasheet.pdf

author: digik
author_rank: Regular Contributor
timestamp: April 27, 2021, 12:56:28 pm
content: Hi, I've tryed circuit in post #6. It produces a single continous beep and it's not very loud, even without the 220 ohm resistor. The single tone is produced only with a 2 uF cap in the ne555 at left and a ~900 ohm resistor instead of the 68K one. So the simulator is completely misleading (as always). How can I produce the beep-beep?

author: pqass
author_rank: Super Contributor
timestamp: April 27, 2021, 04:21:26 pm
content: Quote from: digik on April 27, 2021, 12:56:28 pm2uF+1K is pretty fast for the on/off part. The simulator says it would produce a 333Hz tone. Maybe you mean that for the right 555?I've modified my #6 schematic to use the right 555's pin 3 (output) to drive a 1uF cap and then speaker instead of DIS pin 7.This produced a louder output with Vcc=5V.I've bread-boarded the circuit. See attached image and audio.I've also included scope traces of the on/off waveform (yellow) and zoomed-in tone waveform (green). Probes attached to pin 3 of each 555. The tone is 255Hz; lower than the simulator but the on/off waveform is pretty close.The bread-boarded values are:LEFT 555: 10uF, 56K, HA17555 (Hitachi version of a NE555; apparently NOT CMOS since datasheet shows BJTs!)RIGHT 555: 220nF, 6.7K, MC1455P1 (Motorola version of NE555), 10K pullup on RST.http://www.falstad.com/circuit/circuitjs.html?ctz=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-uOusJuQ7gsHhaliGoCgsEZLh8E+Dw+wgFhO3PaYAEkAHEAAkHxfd9P1vbggA

author: Zero999
author_rank: Super Contributor
timestamp: April 27, 2021, 06:37:29 pm
content: Quote from: pqass on April 27, 2021, 04:21:26 pmThank you for going to the trouble of building it. It sounds pretty good to me.Yes, driving the speaker via an AC coupling capacitor is always better than from a single pull-down transistor. At first it might appear as though a single transistor delivers more power to the speaker, half of it is wasted as heat, as the speaker doesn't use the DC component to make any sound. The 555's output stage will lose a fair amount of power, whilst driving a speaker, but it's still better, than the single transistor option.Did you look at the waveform on an oscilloscope?Have you tried connecting pin 4 of the second 555 to pin 3 of the first?What about using a different IC such as the 74HC14, or 74HC132 and a couple of transistors to drive the speaker?

author: Benta
author_rank: Super Contributor
timestamp: April 27, 2021, 07:04:14 pm
content: Two CD4047 would be a lot easier.

author: ledtester
author_rank: Super Contributor
timestamp: April 27, 2021, 07:09:41 pm
content: Quote from: Zero999 on April 27, 2021, 06:37:29 pmI have to say that I find it easier to design with the 74HC132 / CD4093 quad Schmitt-trigger NAND gate IC. You can find a lot of 4093 circuits on the web and in books such as:CMOS Projects and Experiments: Fun with the 4093 Integrated Circuit by Newton C. BragaThis web page has a few circuits involving a 4093 driving an 8 ohm speaker or piezo.http://www.incbtech.com/index.php/articles/9-projects/1500-experimenting-with-the-4093-nand-schmitt-trigger-art003e

author: pqass
author_rank: Super Contributor
timestamp: April 27, 2021, 09:27:32 pm
content: Quote from: Zero999 on April 27, 2021, 06:37:29 pmIt wasn't much bother. I just wanted to be sure.It occurred to me too [after I tried it] that having both a source and sink would make sure the coil moves decisively back and forth. And with 200mA output capability, it's more than enough to swing the cap+speaker around.See attached waveforms. The yellow probe is on the RIGHT 555 pin 3 (output).The green probe is on the output cap negative/speaker positive side.I changed the timing cap+resistor to 1uF,1K which increased the tone to 347Hz (from my previous scope output).Also, changing the output cap from 1uF to 10uF lowered the frequency to 231Hz.Since the output is also connected to the timing resistor, I'm sure the level of the output cap is screwing with ramp timing waveform.The extra output cap didn't increase the loudness. Mounting the speaker in a box should make it louder.QuoteYes, I've directly attached the LEFT 555 pin 3 (output) to the RIGHT 555 pin 4 (reset) and it does work with my combination of 555's (HA17555 to MC1455); one less pullup resistor.QuoteI'll leave that to someone else to try that combination.You really can't beat a single 556, two timing caps, two timing resistors, one output cap, and a speaker; ubiquitous and compact.

author: Zero999
author_rank: Super Contributor
timestamp: April 28, 2021, 07:31:31 pm
content: Your waveform has a voltage swing of around 3.6V, which is good, because it indicates the model, I linked to above works. Note how the duty cycle and frequency both differ from the theoretical result? If you swapped it for a CMOS 555 timer and added a buffer to drive the speaker, you'll find it will become more symmetrical and closer to the theoretical value.I modified the 4093 circuit linked to by ledtester to show the proper way of driving a speaker, with a pull-push stage.