Hey, I am new to arduino and I am following the guide for Project 5.
It tells you to wire a circuit up with a motor and a potentiometer to control the motor. It explains that you should put a capacitor around the motor because when it starts moving it drains a lot more energy. If the capacitor around the motor keeps everything smooth, what is the purpose of the capacitor around the potentiometer? And is it necessary?
Thanks
A link to the schematic tells a 1000 words ...
// Per.
Zapro:
A link to the shcematic tells a 1000 words ...// Per.
There is no mention of capacitors in the schematic, I can't find an answer on google and since I don't know the terminology to use I don't know what else I am looking for in the schematic.
That's not a schematic it's a data sheet. You need to understand the difference before you can understand what is in your circuit.
petemyster:
There is no mention of capacitors in the schematic, I can't find an answer on google and since I don't know the terminology to use I don't know what else I am looking for in the schematic.
"I am following the guide for Project 5"
Which guide ? Can you post a link, scan a page, take a picture etc. ?
// Per.
Zapro:
petemyster:
There is no mention of capacitors in the schematic, I can't find an answer on google and since I don't know the terminology to use I don't know what else I am looking for in the schematic."I am following the guide for Project 5"
Which guide ? Can you post a link, scan a page, take a picture etc. ?
// Per.
My bad, I didn't think it was a project specific question. The 'Project 5' was just an FYI. Seemed like a general question.
https://skydrive.live.com/redir?resid=B36E309A77704392!4918&authkey=!AODO7tWRCef59DM&v=3
The capacitor in that schematic is across the supply to the microprocessor. It just happens to be across the supply to the pot as well. If you are using Arduino, the capacitor will be on the board.
gm1mfn:
The capacitor in that schematic is across the supply to the microprocessor. It just happens to be across the supply to the pot as well. If you are using Arduino, the capacitor will be on the board.
Thanks. Why is there 2 potentiometers? If the motor causes an initial drain on the power is the capacitor across the motor not enough on its own?
The capacitor on the motor is used to filter out "brush noise". The brushes in the motor are like switches and like switches the "bounce" causing electrical noise. The cap sort of absorbs the noise so that it doesn't cause problems in the circuit.
groundfungus:
The capacitor on the motor is used to filter out "brush noise". The brushes in the motor are like switches and like switches the "bounce" causing electrical noise. The cap sort of absorbs the noise so that it doesn't cause problems in the circuit.
Ok I get it, thanks everyone!
The IC itself also adds noise, because it is also switching inside at a very high speed. It isn't enough to simply put one big capacitor in the circuit, because the wires/traces between parts have inductance and resistance.
Also, the position, number, and value of those capacitors depends on the physical layout of the circuit, something to keep in mind when reading a schematic diagram.
The caps that are installed between the power supply rails (+5 to Gnd) are called "decoupling caps". My rule for decoupling is one 0.1uf cap for each chip as close to the chip's supply and ground pins as possible. You pretty much can't have too many decoupling caps spread around, but you can, easily, have too few .
Really cool insights, I'll be sure to remember them. Thanks all
More insights:-
http://www.thebox.myzen.co.uk/Tutorial/De-coupling.html
petemyster:
gm1mfn:
The capacitor in that schematic is across the supply to the microprocessor. It just happens to be across the supply to the pot as well. If you are using Arduino, the capacitor will be on the board.Thanks. Why is there 2 potentiometers? If the motor causes an initial drain on the power is the capacitor across the motor not enough on its own?
I don't think the motor is an motor, it's an RC servo (looks so on the picture) and the aurdino feeds the servo with an puls 1ms (midposition)±0,5 ms (right/left)
Pelle
Hi, I'm not sure if you can now, but you used to be able to buy 14 and 16 pin IC sockets with 0.1uF caps built in connected betweenpin 14 and 7 or pin 16 and 8.
Those pins were the usual supply pins for most digital gate type IC's.
That way each digital IC had its own decoupling cap, as groundfungus has wisely said.
Tom... 
I think petemyster is referring to one particular chapter in the Arduino Projects Book that comes as part of a starter kit. The other chapters (i.e. projects) don't have a capacitor across the microprocessor. I wonder if the potentiometer supplied with the kit isn't a bit sketchy with spikes of high resistance as the shaft is turned.