Binary input Hex dispaly (7 segment LED)? - Page 2 - Electronic Circuits Projects Diagrams Free

blueroomelectronics · 28th August 2007, 01:42 AM

Most moder PICs have an internal RC clock. Stick with the 16F628A for your project.
Another possible choice but probably a tough find nowadays would be a GAL, PAL or PEEL (no clock needed as it's just a simple logic device)

Mike, K8LH · 28th August 2007, 11:58 AM

Quote:

Originally Posted by dalmation

I was looking at these leds (common cathode):
Attachment 14123

They are about the right size and pinout.

Another thing I meant to ask about the pic... do I need to add an external clock? If so- what frequency range is recommended. There might be a clock pulse available near the binary outputs I can tap into.

Thanks again.

-DAlmation

Those displays will be fine.

No external clock needed. We'll be using the internal oscillator on whichever PICs you procure (16F628A, 16F648A, or 16F88).

dalmation · 28th August 2007, 05:01 PM

I was looking into pricing and availability for the microcontrollers...

Are atmel microcontrollers compatible/comparable to PIC controllers, or are they a totally different animal.

I only ask as the Atmel chips seem to be available at a fraction of the PIC cost?

Thanks.

blueroomelectronics · 28th August 2007, 05:37 PM

The 16F628A is only about $3 qty 1 and less than $2 in slightly larger quantity. Which Atmel chip did you have in mind?

pc88 · 28th August 2007, 05:57 PM

Quote:

Originally Posted by dalmation

I was looking into pricing and availability for the microcontrollers...

Are atmel microcontrollers compatible/comparable to PIC controllers, or are they a totally different animal.

I only ask as the Atmel chips seem to be available at a fraction of the PIC cost?

Thanks.

Atmel chips are not compatible but are comparable with PICs. Both lines of general purpose chips basically have the same capabilities.

dalmation · 28th August 2007, 11:18 PM

I was just looking at some 20 pin atmels on ebay- just checking out the options- I'm more than happy to stick with the pic chips, though.

dalmation · 29th August 2007, 03:02 PM

I was looking over the circuit diagram, and I'm a bit confused...

Here is an edited diagram and the pinout for the pic processor...
Missing info.JPG 16f628A pinout.JPG

Heres what I dont get...

The pic has 15 i/o pins, but it appears I need 17 i/o pins:

8 inputs for the binary bits.
7 outputs for the led segments and
2 outputs to switch between the 2 digits.

Am I missing something there?

Also, there are 8 resistors going from the pic chip to the display? is that just a mistake or am I missing something there too (I thought there should only be 7 as I dont need a decimal point).

Let me know if I'm being daft...

Thanks again.

-DAlmation.

Pommie · 29th August 2007, 03:30 PM

You are not being daft. You have however miscounted the I/O on the pic, it's got 16 I/O lines. As you rightly point out, it appears that you need 17 I/O pins, this is because of the way charlieplexing works. If port B is used to drive the display then it is connected so that bits 2 to 7 go to 6 of the display segments and bit 0 goes to both the unconnected segment on display 1 and display 2's common transistor. Bit 1 goes to the unconnected segment on display 2 and display 1's common transistor.

It might help if you google charlieplexing. Although, the above is not strictly charlieplexing (edit, according to wiki, the above is exactly charlieplexing).

Mike.

dalmation · 29th August 2007, 03:56 PM

If I understand you correctly- there is no way the circuit will function with only 16 i/o pins- I need 17 pins or a different circuit? Is that correct?

Is it is, could I make it work if I replaced the two transistors with 1 component- some form of solid state switch (functioning like a relay, toggling the power from one digit to the other, depending on input being high or low)- all synchronised with the display i/o pins outputting the 2 different characters.

That sound reasonable?

Thanks.

-Dalmation.

Pommie · 29th August 2007, 04:06 PM

No, it will work fine with 16 I/O pins. Google charlieplexing and it should make more sense. Having read what I posted above I can understand your confusion, I should have stated it more clearly.

Mike.

dalmation · 29th August 2007, 05:44 PM

I think I know what you mean now...

basically, like this (g2 being the missing segment of the 2nd digit).
like this.jpg

That look more reasonable now?

I plan to use common cathode LED displays- that will just involve swapping emmitter and collector on transistors- right?

Thanks guys- I appreciate the help.

-DAlmation.

Mike, K8LH · 3rd September 2007, 01:00 AM

Sorry so late.

The Charlieplexed display uses 8 pins for both segments and columns. Just imagine we're using the first two of the eight displays shown in the graphic below.

I hope to start writing that code soon Sir.

Mike

Mike, K8LH · 3rd September 2007, 01:41 AM

Wire the display like this (sorry for the crude drawing);

Can't help you with the Atmel chips. Sorry.

Mike

Mike, K8LH · 3rd September 2007, 08:51 AM

Here's the first draft of the 16F628A firmware (untested). Hope to test it this coming weekend.

Mike

Mike, K8LH · 6th September 2007, 12:53 PM

Eric (Ericgibbs) contacted me off list and he's got a much simpler and more elegant solution that doesn't involve the screwy Charlieplexed display wiring and code. His method uses your suggestion for using 1 pin to drive the common cathodes on both displays.

Thread Tools
Show Printable Version Email this Page
Display Modes
Linear Mode Switch to Hybrid Mode Switch to Threaded Mode

Similar Threads
Title	Starter	Forum	Replies	Latest
Using Oscilloscopes	mechie	Electronic Theory	9	29th November 2007 10:49 PM
driving multiplexed 7 segment display	mathur2000	Micro Controllers	7	24th June 2007 11:08 PM
7 Segment Led Clock using PC signal	vito3693	Electronic Projects Design/Ideas/Reviews	3	18th April 2007 04:22 AM
4-bit binary to decimal into dual 7 segment displays	jupiter669	Electronic Projects Design/Ideas/Reviews	8	15th February 2004 03:06 AM
Convert Leds to 7 Segment Display	Almazick	General Electronics Chat	21	19th August 2003 08:53 PM

28th August 2007, 01:42 AM	(permalink)
blueroomelectronics	Most moder PICs have an internal RC clock. Stick with the 16F628A for your project. Another possible choice but probably a tough find nowadays would be a GAL, PAL or PEEL (no clock needed as it's just a simple logic device) __________________ Bill Smart Kits build Smart People http://www.blueroomelectronics.com

28th August 2007, 05:01 PM	(permalink)
dalmation	I was looking into pricing and availability for the microcontrollers... Are atmel microcontrollers compatible/comparable to PIC controllers, or are they a totally different animal. I only ask as the Atmel chips seem to be available at a fraction of the PIC cost? Thanks.

28th August 2007, 05:37 PM	(permalink)
blueroomelectronics	The 16F628A is only about $3 qty 1 and less than $2 in slightly larger quantity. Which Atmel chip did you have in mind? __________________ Bill Smart Kits build Smart People http://www.blueroomelectronics.com

28th August 2007, 11:18 PM	(permalink)
dalmation	I was just looking at some 20 pin atmels on ebay- just checking out the options- I'm more than happy to stick with the pic chips, though.

29th August 2007, 03:02 PM	(permalink)
dalmation	I was looking over the circuit diagram, and I'm a bit confused... Here is an edited diagram and the pinout for the pic processor... Missing info.JPG 16f628A pinout.JPG Heres what I dont get... The pic has 15 i/o pins, but it appears I need 17 i/o pins: 8 inputs for the binary bits. 7 outputs for the led segments and 2 outputs to switch between the 2 digits. Am I missing something there? Also, there are 8 resistors going from the pic chip to the display? is that just a mistake or am I missing something there too (I thought there should only be 7 as I dont need a decimal point). Let me know if I'm being daft... Thanks again. -DAlmation. Last edited by dalmation; 29th August 2007 at 03:10 PM.

29th August 2007, 03:30 PM	(permalink)
Pommie	You are not being daft. You have however miscounted the I/O on the pic, it's got 16 I/O lines. As you rightly point out, it appears that you need 17 I/O pins, this is because of the way charlieplexing works. If port B is used to drive the display then it is connected so that bits 2 to 7 go to 6 of the display segments and bit 0 goes to both the unconnected segment on display 1 and display 2's common transistor. Bit 1 goes to the unconnected segment on display 2 and display 1's common transistor. It might help if you google charlieplexing. Although, the above is not strictly charlieplexing (edit, according to wiki, the above is exactly charlieplexing). Mike. Last edited by Pommie; 29th August 2007 at 03:48 PM.

29th August 2007, 03:56 PM	(permalink)
dalmation	If I understand you correctly- there is no way the circuit will function with only 16 i/o pins- I need 17 pins or a different circuit? Is that correct? Is it is, could I make it work if I replaced the two transistors with 1 component- some form of solid state switch (functioning like a relay, toggling the power from one digit to the other, depending on input being high or low)- all synchronised with the display i/o pins outputting the 2 different characters. That sound reasonable? Thanks. -Dalmation.

29th August 2007, 04:06 PM	(permalink)
Pommie	No, it will work fine with 16 I/O pins. Google charlieplexing and it should make more sense. Having read what I posted above I can understand your confusion, I should have stated it more clearly. Mike.

29th August 2007, 05:44 PM	(permalink)
dalmation	I think I know what you mean now... basically, like this (g2 being the missing segment of the 2nd digit). like this.jpg That look more reasonable now? I plan to use common cathode LED displays- that will just involve swapping emmitter and collector on transistors- right? Thanks guys- I appreciate the help. -DAlmation.