Question regards Resistors and picaxe..

X

xtech007

Senior Member
Hey Fellas,
I'm trying to get some LEDs to work with a experimental home made board,
I'm using a 18X1, when its installed on the axe090 board with a simple code the LEDs do what they are supposed to do.

But when I place the pic on my home made breadboard it will not.
this is how I have it connected: output pin to resistor(300R) to led to Ground
I'm thinking the problem might be the resistor.
Its 1/2 watt, it seems bigger then the ones provided by the axe090.
Can I use 1/4 watt or is there an standard to be used by the 18x1?

Thanks.
 
K

kevrus

New Member
The wattage of the resistors is a power rating that is referring to its heat dissipation in free air, In your application, just for LEDs, the wattage rating will not be relevant.

Are you sure that you have the value correct, colour coding should be orange, black, brown plus tolerance for 300R. Make sure its not orange, black, orange which is 30K(some oranges can look brownish, and vice versa). Also check LED orientation and all wiring/connections
 
A

alband

Senior Member
erm, could be just a typo, but are you sure you're using an 18X1?:confused:

It's just that this chip doesn't exist (I think). There is an 18, an 18A, 18X, 28X1 and 40X1 but no 18X1...
 
S

superworm

New Member
I agree with kevrus, made the mistake many times due to bad resistor markings. Get the multimeter out and check the resistance manually. Also check the orientation of the LEDs.

You might possibly want to put your multimeter on the output pin of the PICAXE you are trying to use, make sure it is switching HIGH when specified.
 
T

Tinhorn

New Member
Do have a resister between the Serial-In Pin and ground? You need teh 22K/10K resistance circuit or at least something like 47K to ground.....
 
S

superworm

New Member
@ Tinhorn

It's best to use a 10K resistor from the serial in pin to ground. It's standard practice, tried and tested.
 
W

westaust55

Moderator
xtech007 said:
Hey Fellas,
I'm trying to get some LEDs to work with a experimental home made board,
I'm using a 18X1, when its installed on the axe090 board with a simple code the LEDs do what they are supposed to do.

But when I place the pic on my home made breadboard it will not.
this is how I have it connected: output pin to resistor(300R) to led to Ground
I'm thinking the problem might be the resistor.
Its 1/2 watt, it seems bigger then the ones provided by the axe090.
Can I use 1/4 watt or is there an standard to be used by the 18x1?

Thanks.
Click to expand...
Power (Watts) = I * I * R (Amps * Amps * Resistance)
also
Power (Watts) = Volts x AMps

Therefore with a 330 Ohm resistor the current at 5V is limited to around 12 mA so
P = 0.012 * 0.012 * 330 = 0.047 Watts.

So a 1/4W (0.250W) resistor will be fine - which is the case for almost any purely logic circuits.

Presuming the resistors are 300 Ohm then have you got the LED's connected the right way around?
 

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