The Raspberry Pi Thread [4]

alphanumeric said:

I have to correct what I aid above, I'm using 22 ohms not 220. They are Red, Red, Black. As near as I can tell anyway, I don't have an ohm meter handy to measure them. I'm partially color blind and they are behind a diffuser.

Ok. Thanks.
One more question. What is the most common diameter of heat shrink tubing you usually use? I need to get some.

badrobot said:

Ok. Thanks.
One more question. What is the most common diameter of heat shrink tubing you usually use? I need to get some.

The last tubing I bought was a multi pack with all different sizes. I'd have to measure the one I think I use the most. A lot of times I use more than one size. It depends on the gauge of wire I'm covering etc.

EDIT: Same deal with resistors, I just by a pack with all different values.

alphanumeric said:

The last tubing I bought was a multi pack with all different sizes. I'd have to measure the one I think I use the most. A lot of times I use more than one size. It depends on the gauge of wire I'm covering etc.

Yeah, I saw a lot of multi pack tubing but I am sure, for small wiring projects, more than half of it is useless.

As for resistors, it's ok to get diff values as you don't really know what you'll need.

If you look at the guides for turning on an LED via the Pi GPIO they show 330 and 470 ohm resistors? I guess that's why I thought mine were 220 ohm. Best guess as why the high values is so you don't draw to much current from the GPIO, they have a limit. My LED's are driven by Darlington transistors from 5V. Totally isolated from my Pi. The Pi just turns on the transistor.

badrobot said:

Yeah, I saw a lot of multi pack tubing but I am sure, for small wiring projects, more than half of it is useless.

As for resistors, it's ok to get diff values as you don't really know what you'll need.

I would say you want something about the diameter of a pencil or bic pen? Even just a little smaller should be Ok.

If I did my math correctly I'm driving my LEDs with 77ma. 1.7V/22 ohm = 0.077 A. I = E / R Been doing it for a while and they haven't burned out.

alphanumeric said:

If you look at the guides for turning on an LED via the Pi GPIO they show 330 and 470 ohm resistors? I guess that's why I thought mine were 220 ohm. Best guess as why the high values is so you don't draw to much current from the GPIO, they have a limit. My LED's are driven by Darlington transistors from 5V. Totally isolated from my Pi. The Pi just turns on the transistor.

220 ohm is correct if your Vf is 3.3 and source voltage is 18v.

Mine is 68 ohm with 3.4Vf and 5V source.

http://led.linear1.org/1led.wiz

Installed...

badrobot said:

220 ohm is correct if your Vf is 3.3 and source voltage is 18v.

Mine is 68 ohm with 3.4Vf and 5V source.

http://led.linear1.org/1led.wiz

It's been a while since I wired that all up. Taking a quick glance in I could see the Red Red Black and in my head I came up with 220, but its actually 22.0. Black when its the multiplier band means no zero, or times 0. Brown would be one zero or times 10 and 220. Red would mean add 2 zeros 2200 etc. My brain I think came to a preconceived notion that it must be 220, not 22.

My LED's are driven from 5V but turned on with the Pi's 3.3V GPIO signal. 3.3V isn't enough to drive some LED's, depending on what color they are etc. I used this, https://www.adafruit.com/product/757 to drive the LED's. 3.3v on one side and 5V on the other side. Very minimal current draw from the Pi's GPIO. Nice and safe.

Just a FYI post. It looks like the 1 per customer restriction on Pi Zero's is still in effect. =( On Adafruit and Pimoroni anyway. If I try to add a second I get the warning when I look at my list of items in my cart. Even if one is a kit and the other a single. You can though, buy 1 Zero and 1 Zero W on the same order. If your so inclined and have a project that doesn't need WIFI. I know, "why would you want a regular Zero", don't shoot the messenger.

EDIT: Looks like you can order a Zero W and a Zero W with header on the same order? No red flags/messages in my cart? I can't actually place the order yet though, not till payday.