Hello,
I just finished a digital clock with temperature using an adafruit led backpack, 1307 RTC, and a DS1820 temperature sensor. I want to thank adafruit tech support for my success. I want to take that same design and use bigger seven segment displays (12" or more) and using the backpack or build one. I experimented with it and using TIP31 transistors to switch the digits using 24v. My question is that should I use an adafruit led backpack with the seven segment display that come with it or should I build a backpack of the same type from scratch? My students want to build this as a IEEE club project. Can you point me in the right direction as to the circuit and schematic for the led backpack? I will post the current digital clock and temperature project. Thanks, Curtis
LED Backpack
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- adafruit_support_bill
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- Joined: Sat Feb 07, 2009 10:11 am
Re: LED Backpack
There are a few ways to go - depending on how your leds are wired.
Are these off-the shelf 7-segment displays, or are you fabricating them from discrete leds or led strips?
Are these off-the shelf 7-segment displays, or are you fabricating them from discrete leds or led strips?
- curtisd
- Posts: 24
- Joined: Fri Mar 21, 2014 10:41 am
Re: LED Backpack
I am looking at some 16" common-anode single segment displays. I wanted to replicate your backpack or use yours without the four segment attached. How do I wire the 4 single large SSD to add to adafruit backpack or can I make backpack from scratch. I know I will have to use a power transistor to use the 24 v needed and just 5 v to the backpack. Thank you
Curtis
Curtis
- adafruit_support_bill
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- Joined: Sat Feb 07, 2009 10:11 am
Re: LED Backpack
These boards will drive 24 channels of leds at up to 30v: https://www.adafruit.com/product/1429
You can chain them to get more channels.
You can chain them to get more channels.
- curtisd
- Posts: 24
- Joined: Fri Mar 21, 2014 10:41 am
Re: LED Backpack
Hi,
I read about that on your link, Thanks. Can this board replace the SSD backpack? I see it can drive a large number of leds. Thanks, Curtis
I read about that on your link, Thanks. Can this board replace the SSD backpack? I see it can drive a large number of leds. Thanks, Curtis
- adafruit_support_bill
- Posts: 88153
- Joined: Sat Feb 07, 2009 10:11 am
Re: LED Backpack
It drives from the high-side, so it could drive the common anodes. But the max current is limited to about 60mA, so it might struggle if too many segments were lit. You would still need some transistors to do the low-side switching of the segments.
There are quite a few dedicated led drivers available with various voltage and current capabilities. Here's a page from the Mouser catalog showing some of the Maxim offerings.
http://www.mouser.com/catalog/645/usd/89.pdf
There are quite a few dedicated led drivers available with various voltage and current capabilities. Here's a page from the Mouser catalog showing some of the Maxim offerings.
http://www.mouser.com/catalog/645/usd/89.pdf
- curtisd
- Posts: 24
- Joined: Fri Mar 21, 2014 10:41 am
Re: LED Backpack
Thanks for the info. Could I take a backpack SSD and instead of putting the 4 digit SSD I solder connections (wires) to where it come on and use power transistors with a resistor on the base from the backpack and pass 12v or 24v to light up big SSD? Also How would I wire the 4 SSDs together? I think I solder all the cathodes (a-g plus DP) (Common Anode) together in parallel and switch all the anode per segment. Thanks for all your effort.
Curtis
Curtis
- adafruit_support_bill
- Posts: 88153
- Joined: Sat Feb 07, 2009 10:11 am
Re: LED Backpack
These displays are multiplexed, so you don't need a 28 pins to drive 4x7 segments. You just need 4 pins to control the common anodes and 7 pins to control the 7 segments. The chip will cycle through the 4 digits, pulling one anode at a time high and pulling the cathodes corresponding to the active segments in that digit low.
You would need 4 PNP transistors for the common anodes and NPN transistors for the 7 cathodes.
You would need 4 PNP transistors for the common anodes and NPN transistors for the 7 cathodes.
Please be positive and constructive with your questions and comments.