Some Arduino starter-kit projects show the resistor placed before the anode of a LED, coming from output, and others show it after the cathode, going to the ground. Is there any difference? Why?
Electronic – Resistor on anode or cathode?
led
Related Solutions
Setting the PWM duty cycle to 255 is the opposite of the digital write with low. The duty cycle of 255 means the pin is driven high (5v) 100% of the time. I suspect if you reverse your logic of the Analog writes you will get your intended results.
Things regarding a high side switching of a voltage higher than the control voltage are not as simple as they seem.
Take for example the following circuit controlled with an Arduino I/O pin
When the I/O pin is LOW the voltage to the base will be 0, that means that the Vbe will be 9v and since it is >0.7v the transistor will be on.
When the I/O pin is HIGH the voltage to the base will be 5v, that means that the Vbe will be 4v and since it is >0.7v the transistor will also be on.
So basically that configuration can't work as a switch because the transistor will always be on.
In order to make a circuit like the above work properly you have to add a level translator that will actually drive the base with 0v and 9v (or whatever the collector voltage level is), a circuit like
One alternative of a working single transistor high side circuit is an emitter follower like
The problem is that in this case the emitter will follow the base voltage when the transistor is on so for 0 and 5v control voltage you will get 0 and 4.3v output irrelevant of the voltage connected to the collector (within transistor specs of course) which may ot may not suite your specific application.
Another alternative is to use a device like ULN2003/2803 but intended for high side switching. Such a device is UDN2981 which has 8 source drivers like the following and can be used as a high side switch controlled by TTL level logic.
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Best Answer
There's no difference.
One of the basic principles of electric current is that the same current flows through all elements that are arranged in series.
simulate this circuit – Schematic created using CircuitLab
The purpose of the resistor is to limit the current, it doesn't matter in which part of the circuit it is located.
In the case of throwies, the internal resistance of the coin-cell battery is used as a current limiting resistor.
simulate this circuit