Bounce Servo with 555 timer

Is it possible? Yes. Would I recommend a 555 for this application, no.

Consider that you will need to generate a PWM waveform sweeping from a 5% dutycycle to 10% dutycyle depending on the servo.

As @scottiebabe points out it is a bit tricky but possible to do with 555 timers. You could make the middle waveform with a 556 (dual 555) - one 555 would generate a continuous square wave with 20 ms period. The second 555 would be a one-shot triggered by the first 555 - it creates the 2 ms pulse shown in the middle waveform. A third 555 would be used to generate a 1 second pulse when the button is pushed to change positions. The output of the third 555 would drive a diode and resistor connected to the timing capacitor of 555 #2 so that its pulse width changes to 1 ms for one second. (the last waveform)

It can also be done with just two 555s but the frequency might vary a bit.

Is there a more elegant solution to this?  I have only touched the surface of small electronics and may have got hung up on the name 'timer' thinking that was the best solution.  I also saw something of interest where the servo was physically modified and performed without pwm.

Beauty is in the eye of the beholder. If you decide to use 555 timers you could submit your design to the 555 timer contest on hackaday.

I recently used a RPI Pico to enable a PWM output after a button press it was too easy. Just a few lines a code and done.

A little microcontroller is a reasonable solution. The only challenge with the 555 or discrete logic in general is it isn't a cookbook application and may be a bit daunting depending on your experience.

Thanks for the feedback.  I am pursuing it with an Arduino now.  I can picture the final project having user input of pushing the button more than once to adjust the delay.  I did learn a touch along the way though.  Hoping to post in here with a completed project before 2022. 

Sounds like a fun project. If you hit any snags, there are lots of members happy to help. Happy making!

If you were to use a MOSFET as a crude monostable, with resistor, capacitor, and switch, for the seconds timing, it could be done with just one 555 for the servo waveforms. I don't think the frequency variation matters with a servo (within limits, of course) - it's only looking for the pulse width.

Does this do what you wanted (sorry the video is a bit blurry)?

Here's the circuit and the build on a breadboard

the start position is controlled by the 1k resistor under the 1N4148, the end position by the 470n capacitor
controlled by the MOSFET (I actually used two 470n in parallel, so the circuit value's wrong), and the delay time
after the switch is released is set by the 150k and the 10u.

These are the output waveforms going to the servo, in case you're interested. First is the rest position, the second
the position when the switch is pressed.

Anyway, it will give you something to play with if you're interested in experimenting with a 555.

Neat little circuit. I wonder if I can upload .asc files on the new website. In the holiday spirit I put JC2048's deign into LTSpice for one to experiment with too.

Version 4
SHEET 1 880 792
WIRE -320 -32 -544 -32
WIRE 0 -32 -320 -32
WIRE 192 -32 0 -32
WIRE 368 -32 192 -32
WIRE -320 0 -320 -32
WIRE -320 96 -320 80
WIRE -224 96 -320 96
WIRE -192 96 -224 96
WIRE 80 96 48 96
WIRE 368 96 368 -32
WIRE 368 96 304 96
WIRE -320 128 -320 96
WIRE -192 128 -192 96
WIRE 80 160 -96 160
WIRE 448 160 304 160
WIRE -768 176 -768 144
WIRE -320 224 -320 192
WIRE -192 224 -192 192
WIRE 80 224 -32 224
WIRE 448 224 304 224
WIRE 0 288 0 -32
WIRE 80 288 0 288
WIRE 352 288 304 288
WIRE -544 336 -544 -32
WIRE -320 336 -320 304
WIRE -240 336 -320 336
WIRE -192 336 -192 304
WIRE -192 336 -240 336
WIRE -96 336 -96 160
WIRE -96 336 -192 336
WIRE -592 352 -720 352
WIRE 352 352 352 288
WIRE -320 384 -320 336
WIRE -192 384 -192 336
WIRE 48 416 48 96
WIRE -720 432 -720 352
WIRE 352 448 352 416
WIRE -544 480 -544 416
WIRE -192 512 -192 448
WIRE -320 528 -320 448
WIRE -32 528 -32 224
WIRE 464 528 -32 528
WIRE -720 544 -720 512
WIRE -544 608 -544 560
WIRE -448 608 -544 608
WIRE -368 608 -448 608
WIRE -544 640 -544 608
WIRE -448 640 -448 608
WIRE -320 672 -320 624
WIRE -544 752 -544 720
WIRE -448 752 -448 704
FLAG 48 416 0
FLAG 352 448 0
FLAG 192 -32 VCC
FLAG 448 160 DISCHARGE
IOPIN 448 160 Out
FLAG -192 512 0
FLAG -320 672 0
FLAG -240 336 CAP
FLAG 448 224 CAP
IOPIN 448 224 BiDir
FLAG 464 528 OUT
IOPIN 464 528 Out
FLAG -544 752 0
FLAG -448 752 0
FLAG -592 400 0
FLAG -768 176 0
FLAG -720 544 0
FLAG -768 64 VCC
FLAG -224 96 DISCHARGE
SYMBOL Misc\\NE555 192 192 R0
SYMATTR InstName U1
SYMBOL cap 336 352 R0
SYMATTR InstName C1
SYMATTR Value 100n
SYMBOL res -336 -16 R0
SYMATTR InstName R1
SYMATTR Value 1.2k
SYMBOL res -336 208 R0
SYMATTR InstName R2
SYMATTR Value 1k
SYMBOL res -208 208 R0
SYMATTR InstName R3
SYMATTR Value 10k
SYMBOL diode -304 128 M0
SYMATTR InstName D1
SYMATTR Value 1N4148
SYMBOL diode -176 192 R180
WINDOW 0 24 64 Left 2
WINDOW 3 24 0 Left 2
SYMATTR InstName D2
SYMATTR Value 1N4148
SYMBOL cap -208 384 R0
SYMATTR InstName C2
SYMATTR Value 470n
SYMBOL cap -336 384 R0
SYMATTR InstName C3
SYMATTR Value 470n
SYMBOL nmos -368 528 R0
SYMATTR InstName M1
SYMATTR Value AO6408
SYMBOL cap -464 640 R0
SYMATTR InstName C4
SYMATTR Value 10�
SYMBOL res -560 624 R0
SYMATTR InstName R4
SYMATTR Value 150k
SYMBOL res -560 464 R0
SYMATTR InstName R5
SYMATTR Value 1k
SYMBOL sw -544 432 M180
SYMATTR InstName S1
SYMATTR Value SX
SYMBOL voltage -720 416 M0
WINDOW 123 0 0 Left 0
WINDOW 39 0 0 Left 0
SYMATTR InstName V1
SYMATTR Value PULSE(0 1 2 0 0 100m 1 1)
SYMBOL voltage -768 48 R0
WINDOW 123 0 0 Left 0
WINDOW 39 0 0 Left 0
SYMATTR InstName V2
SYMATTR Value 6
TEXT -72 728 Left 2 !.model SX SW(Ron=.1 Roff=1G Vt=0.5 Vh=1m)
TEXT -930 776 Left 2 !.tran 10
TEXT -392 -104 Left 4 ;JC2048 E14 Servo Design

No luck with .asc, I had to add a .txt extension.

Thanks. An even easier way to experiment with it.

It's interesting that there are all these spice models for 555 timers. Tina-TI has several in the part libraries that it comes with.

Whilst I'm thinking about it, if anyone wants to actually build it, I used a BS170 for the MOSFET [a 2N7000 would also be fine]. I also had a 10uF electrolytic across the supply rails at the breadboard end - the servo is noisy (electrically), but it worked ok with a 6V supply. That was a small 'micro' servo. It might not be so happy with a larger one.