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- Posts: 143
- Joined: Tue May 12, 2015 7:03 pm
I remember talking to you about using Shift registers to drive seven segment displays, but not being able to do the 16 segment displays (for the obvious reason of too many pins). I am using the older 2n2222 discrete npn individual transistors to drive the large 6.5 inch seven segment displays, because I have a lot of them here. I looked to see if Parallax carries the ULN2803 IC , and they do. If memory is correct, a Darlington transistor is a npn connected to a npn transistor, to handle more current. Not sure if they come in the pnp style. The ULN2803 seems to also include flyback diodes for handling voltage spikes, when switching inductive loads. Since Parallax is having a sale I'll order some with other stuff and learn a New IC.
The 6.5 inch seven segment display's are common Anode (they all share the Positive input). The forward current is 20 mA and forward voltage is 12 volts.
I am very interested in the article you hope to have published.... will it most likely be in Nuts & Volts? Maybe you'll make the cover again...
When you say offset, do you mean the offset as in, page 76 in the book Smart Sensor Text version-v1.0pdf ?
I'm still working on the project and only got one of the large display counting in seconds, but it was working and is very bright..., I can't imaging how bright 6 of them will be.
- Posts: 404
- Joined: Tue May 12, 2015 2:43 pm
- Location: Palmyra, NY
The reason the shift registers don't work real well for the 16-segment displays is that most are actually 17-segment. Two 8-bit shift registers give you only 16 outputs.
The Darlingtons are NPN, but if your displays are Common-Anode (CA) then that's what you want. You want to drive the low side (Cathode). So the ULN2803 is exactly what you need to consolidate parts. You don't need to connect the COM line for the diodes since LEDs are not inductive devices.
Nuts and Volts or Servo. Waiting for a reply back now. I just got my website mail working right again. Apparently I was missing a few aliases.
When I say offset, what I mean is that when you want to put a value on the 7-segment display the subroutine that handles it takes the value and adds it to a base address of a lookup table that has the patterns for your display (numbers). So when you pass the value on to that subroutine it grabs each pattern based on the offset (value) and shifts that pattern out to the shift register for that digit. Pretty simplistic and efficient and all digits can use the same pattern lookup table.
I'm only responsible for what I say, not what you understand.
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