General > General Technical Chat
Is the 555 still a viable IC?
Zero999:
--- Quote from: baldurn on February 19, 2024, 10:08:32 pm ---
--- Quote from: Zero999 on February 19, 2024, 07:12:06 pm ---
--- Quote from: factory on February 19, 2024, 05:39:22 pm ---Bigclive found a new product using the 555 only 2 years ago.
David
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It uses the 555 as a Schmitt trigger oscillator to generate a sawtooth, which compared against a potentiometer, using a comparator to generate PWM. I would have used a quad op-amp/comparator IC: one channel for the Schmitt trigger oscillator and the rest as comparators for the PWM. The LM339 will directly run off 24V, so no voltage regulator is required.
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The 8 pin ATTiny212 would have done the job with one chip instead of three chips and a much simpler schematic. You would configure three pins as ADC to sample the potentiometers and three pins as PWM output. The remaining two pins are VCC and GND.
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That would be two ICs, since the MCU requires a 5V regulator.
Unless it's just a hobby project, I would be hesitant at using an MCU for such an application because there's only one supplier and the firmware cost. The LM339, is just one IC, which runs directly off 24V, is cheaper than any MCU and can be bought from multiple suppliers. The only downside is more passive components are required, but they're very cheap.
--- Quote from: SiliconWizard on February 19, 2024, 09:35:59 pm ---Definitely consider the TLC variant which is under $1 per 1 at Digikey, $0.37 per 1, $0.23 per 100 at LCSC. It's also better on almost all counts than the original.
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The downside of the TLC variant is the output is much weaker, than the NE555. It can only source 10mA, which isn't enough to drive a relay and will considerably slow down the turn on time of a MOSFET. It can sink 100mA, but sometimes sourcing is required because the relay or driver transistor needs to be on, when the output is high.
https://www.ti.com/lit/ds/symlink/tlc555.pdf
AndyBeez:
I recently encountered a 556 (dual 555) on a plug-in mouse scarer. One stage provided a low frequency pulse that gated the second stage; which ran 40KHz into a transducer. The DIL packaged chip was dated c.2010, so there were a few analogue diehards out there. But they possibly have long retired, leaving mouse scaring to the Arduino kids.
baldurn:
--- Quote from: Zero999 on February 20, 2024, 11:17:18 am ---
--- Quote from: baldurn on February 19, 2024, 10:08:32 pm ---The 8 pin ATTiny212 would have done the job with one chip instead of three chips and a much simpler schematic. You would configure three pins as ADC to sample the potentiometers and three pins as PWM output. The remaining two pins are VCC and GND.
--- End quote ---
That would be two ICs, since the MCU requires a 5V regulator.
Unless it's just a hobby project, I would be hesitant at using an MCU for such an application because there's only one supplier and the firmware cost. The LM339, is just one IC, which runs directly off 24V, is cheaper than any MCU and can be bought from multiple suppliers. The only downside is more passive components are required, but they're very cheap.
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For this extremely simple purpose, you could probably get away with just a resistor and a diode for a voltage regulator accepting anything between 6 to 24 volts. The total BOM could be 1 resistor, 1 diode, 1 MCU, 3 MOSFET, 3 pots. But I am not convinced this is a real product - frankly it looks like a beginner project for DIY :-)
Anyway, using an op amp for saw tooth is not an example of the usefulness of the 555 chip.
MT:
5:23 Big Clive about the 555 quote: "its ancient, one of the earliest "micro controllers", goes back long long way. :-//
https://youtu.be/0WHFwqzyu0U?t=322
Interview with Hans Camenzind inwentor of 555.
http://www.semiconductormuseum.com/Transistors/LectureHall/Camenzind/Camenzind_Page2.htm
https://www.planetanalog.com/at-50-years-the-555-timer-ic-defies-conventional-wisdom/
--- Quote from: factory on February 19, 2024, 05:39:22 pm ---Bigclive found a new product using the 555 only 2 years ago.
David
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PlainName:
--- Quote from: AndyBeez on February 20, 2024, 01:05:43 pm ---I recently encountered a 556 (dual 555) on a plug-in mouse scarer. One stage provided a low frequency pulse that gated the second stage; which ran 40KHz into a transducer.
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Sounds like a perfect use for one (albeit dual). Just does what it's meant to and you don't have to worry about battery voltage or anything.
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