## Introduction: 555 Useless Machine

What is useless machine? It is machine that haven't anything to do, it is just for making useless things. Like switching off switch :)

## Step 1: Parts

- 555 timer I think that you can buy it in any electronics shop, this is head of our useless machine

- Servo, the most popular small micro servo you can find it in RC shops or electronic, it will switch off our switch

- Lever switch, it's important because we will switch it off with servo so it can't be any other type of switch

- resistors, I will tell you values in next steps

- capacitor 100nF

- diode (not LED, rectifier diode)

- batteries (1 cell lipo, or 2 AA batteries)

## Step 2: Some Math

On the above photos you see how I calculate resistors values.
I spent 2 hours on calculating values for resistors and all the time I got minus resistance which is impossible I don't know what is wrong. Next day after like hour of searching in google I found that if high state is shorter than low we need to add diode and change formulas a little bit :)

Servo is controlled with 50Hz PWM signal, if we set high signal in this pwm for 1.5ms servo will go to 90 degrees, if you set 2ms it will go to 180 and 1ms to 0 degrees. So when switch is off as high signal I get 1ms and as low signal 19ms together it is 20ms (0.02s) to get the frequency you need to divide 1/0.02 = 50Hz. When switch is turned on I just change high signal to 2ms and low to 18ms. I hope you understand it :) if you want to know more, google 555 and you should find plenty of good tutorials about it.

## Step 3: Simulation

While I waited for my parts I started simulating my design in circuits.io. It went very well and everything is working. BTW circuits.io is great program it shows you that servo is moving or if you give to big voltage to LED. In my circuit I added oscilloscope to see the signal while experimenting with resistors. Here is link to mys design if you want to check it out:

https://circuits.io/circuits/3227397-555-useless-machine

## Step 4: Scheme

Here is the schema from circuits.io and eagle (I made an eagle schematic to mill a PCB for it, while writing this instructable I found export to eagle option in circuits :)) Below you can find resistors values, they are a litle bit diferent than calculated because there are no as precise resistors, It is possible that you should experiment with resistors values to get it working because resistors are not ideal and have 5% tolerance of value.

C1 = 100nF

R1 = 10 000

R2 = 0

R3 = 247 000

R4 = 16 400

## Step 5: 3D Files

For my useless machine I had made 3D printed enclosure. If you want you can make it out of wood (it will looks much more better) unfortunately I am not talented in hand making things, so I just designed and printed it.

## Step 6: Assembling

Begin with assembly flap with top, is to this you need to use piece of filament (diameter of 1.75) or something similar. Then to top you can screw on micro servo and switch. For screwing servo you should use M2 screws at least 8mm long. To screw arm you should use again M2 screw and screw it on very strongly.

## Step 7: PCB

I also made PCB for my machine, I like making PCBs, if you don't just solder it like leg to leg or something I don't know how to say it, just without PCB :D This is my first milled PCB, instead of thermotransfer methodod I decided to mill it with small CNC machine. And at least for this PCB this method is much better because you don't need to deal with ironing it and using acid. But I am aware that milling small traces and pads for SMD componnents can be impossible.

## Step 8: Enjoy It!

Right now you can use this super machine to make something creative, to change the world, or no, this is just useless thing that turns off itself. But I learned a lot during building it so maybe it is not so useless? And don't forget how many fun it can gives you :D Thanks for reading!

Runner Up in the
Design Now: 3D Design Contest 2016

Participated in the
Circuits Contest 2016