The 555 timer is sometimes referred to as „the time machine“. It has historically been of great importance in the generation and detection of temporal signal sequences.
Before discussing the device itself, the various modes should be briefly considered:
Mode^other name^explanation^application^examples^
| astable | oscillator, multivibrator | output signal changes value periodically | creation of a periodic, rectangular signal, with adjustable pulse width and frequency | motor control, dimming of LEDs, generation of tones |
| monostable | „flip-flop“, monoflop | Output signal is triggered by a trigger and goes back to 0V after a defined time | Extending pulses that are too short, setting a fixed pulse length | Conditioning sensor signals of a proximity sensor |
| bistable | flipflop | set/reset when thresholds are exceeded/fallen short | bounce-free switch, circuits with hysteresis | two-point controller, e.g. for heating elements |
It can be seen that there are a wide variety of applications for this component. The question can be asked what differentiates the application of this component from a microcontroller:
| Property | Microcontroller | Timer 555 | ||
|---|---|---|---|---|
| Cost (single unit, 2018) | from 3ct (chin. µC, PADAUK PMS150C) | from 29ct (western µCATtiny) | ||
| cost (>10'000, 2018) | from approx. 2..3ct (chin. µC) | from 20ct (westl. µC) | from 2..3ct | |
| other components | interference suppression | interference suppression | transistors, resistors and other capacitors | depending on the application |
| Complexity | in software | hardly available | ||
| Flexibility | Updates possible | if potentiometers were used, limited | ||
| advantages for small quantities | easily changeable by programming, \no component scattering | easily changeable by reassembling on the board, \no software bugs, \no tools necessary |
For a long time, the Timer 555 was the most cost-effective solution for the tasks mentioned above. Currently (2018), Timer 555 and microcontroller prices are about the same in large quantities. Nevertheless, due to its simplicity, the Timer 555 is still found in various consumer electronic products.