Neopixel Voltage Drop
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- brentswanee
- Posts: 9
- Joined: Tue Mar 21, 2017 9:09 pm
Neopixel Voltage Drop
I have a circular cloth eyeball that I want to place 36 pixels in three rings around in the Iris. I am powering it with a 3.7V lipo 4400 mAh to my flora connected to one data pin. My original plan was to have a continuous data line through all 36 using 3 ply conductive thread but know there could be significant voltage drop after 20 neopixels. What type of measurable resistance from pixel to pixel should I be seeing? In the inner most ring (shortest distance between neopixels) I am seeing 0.8 ohm but I know its a cumulative loss so how much is too much?
- adafruit_support_bill
- Posts: 88088
- Joined: Sat Feb 07, 2009 10:11 am
Re: Neopixel Voltage Drop
You will have the loss due to the relatively high resistance of the thread (about 16 ohms per foot). And you will also have the contact resistance of the connections. The resistance of the connections is highly variable depending on the cleanliness of the contacts and how tight the knots are.
The best way to minimize voltage drops is to feed power to multiple points on the string of pixels. With 36 pixels I'd feed power to at least the beginning and end of the string. You can do that by just running the power and ground threads at the end of the string all the way back to your Flora. That means no pixel is more than 18 pixels away from the power source.
The best way to minimize voltage drops is to feed power to multiple points on the string of pixels. With 36 pixels I'd feed power to at least the beginning and end of the string. You can do that by just running the power and ground threads at the end of the string all the way back to your Flora. That means no pixel is more than 18 pixels away from the power source.
- brentswanee
- Posts: 9
- Joined: Tue Mar 21, 2017 9:09 pm
Re: Neopixel Voltage Drop
That is definitely something I will do then. I was fairly concerned about the data pin itself or does the voltage connection keep that a steady output voltage?
The reason being is I have several wheels of the 2 ply and 1 of the 3 ply. Best to keep the + and - connections 3 ply and the data 2 ply?
The reason being is I have several wheels of the 2 ply and 1 of the 3 ply. Best to keep the + and - connections 3 ply and the data 2 ply?
- adafruit_support_bill
- Posts: 88088
- Joined: Sat Feb 07, 2009 10:11 am
Re: Neopixel Voltage Drop
Voltage drop is not an issue for the signal wire because there is very little current flow. (The voltage drop is equal to the resistance in Ohms multiplied by the current in Amps).
So 3-ply for power & ground and 2 ply for the signal should be fine. Just be sure to tie all those knots good and tight!
So 3-ply for power & ground and 2 ply for the signal should be fine. Just be sure to tie all those knots good and tight!
- brentswanee
- Posts: 9
- Joined: Tue Mar 21, 2017 9:09 pm
Re: Neopixel Voltage Drop
Thank you for your help. I am excited to do my first wearables project!
Please be positive and constructive with your questions and comments.