Sequential LED driver. - Page 2

cpemma · 11th August 2004, 09:41 PM

For bar mode only, I'd think a raft of quad opamps (LM324) or comparators (LM339) would work out far cheaper than using several LM3914 chips.

You could run the chips off say 18V and chop say a regulated 15V up with a resistor chain to use as the references for each level. A pot on the supply gives you the comparison voltage.

gmphadte · 12th August 2004, 05:09 AM

If you are not interested in voltage and only interested in DOT mode, then you should use 4017s in a tricky way.

This was the need in one timer and I wanted to indicate the step number by a glowing LED. The oscillator was made programmable using ICM7217. This is something like a programmable mechanical street light timer.

The trick...

Follow carefully
LED 9(at pin 11) is not connected in all 4017s

The pin 11 is utilised to disable the present chip though an EX-OR gate and enables the next through another EX-OR. One input of the first EX-OR ic is tied high(can be looped also).The EX-OR output goes to clock inhibit (pin 13).

tie all resets together and all clock pins together. Get your clock and reset with large fan-out

Pin 11 will go to one i/p of self EX-OR and one i/p of next EX-OR

You want them to come back and forth, then place the LEDs wherever you want.

LED No.1-No.50-2-49-3-48-4-...

Gajanan

imix500 · 12th August 2004, 07:15 AM

Hi gmphadte, i see you've found the other thread.
To Moderators: I didn't mean to start two threads on the same subject- my appologies.
cpemma, that's another great idea. Would a LM324 or something similar be ok with outputting dc? Would it be stable driving a load such as an led? I've never used one for anything other than audio. The 3914's are under $2 each and they include everything I'd need to have a working display, but the op amp idea is interesting- might be easier to configure for custom trigger levels. Hmmm.

gmphadte · 12th August 2004, 11:41 AM

You have to use LM339, a quad comparator with open collector. Typical output sink current is 16 mA.

Connecting a currenr source instead of resistors for LEDs will save lot of wiring trouble. Connect a ladder made from LEDs to the outputs, below the cc source. Being open collector the output transistor that conducts will prevent others from lighting.

Vcc--16 mA CC source--LED1 A - LED1 K--*--LED2 A - LED2 K--*--LED.....

Use higher Vcc to make a longer chain

K-cathode
A-anode
* Comparator o/p goes here
Ground is not connected

Gajanan

cpemma · 12th August 2004, 04:03 PM

Quote:

Originally posted by imix500
Would a LM324 or something similar be ok with outputting dc?

It can be connected as a comparator, no feedback resistor, just the reference voltage to one input, voltage signal to the other. Output swings from 0V to (Vs-1.5) on a single rail supply, IIRC will source 20mA OK. See the datasheet to check.

imix500 · 13th August 2004, 02:41 PM

Gotcha. That's a pretty cool idea. I'm gonna breadboard a few of these and see how they do. Thanks!

12th August 2004, 05:09 AM	#12
gmphadte diyAudio Member Join Date: Jul 2003 Location: Dona paula, Goa	sequential LED in DOT mode If you are not interested in voltage and only interested in DOT mode, then you should use 4017s in a tricky way. This was the need in one timer and I wanted to indicate the step number by a glowing LED. The oscillator was made programmable using ICM7217. This is something like a programmable mechanical street light timer. The trick... Follow carefully LED 9(at pin 11) is not connected in all 4017s The pin 11 is utilised to disable the present chip though an EX-OR gate and enables the next through another EX-OR. One input of the first EX-OR ic is tied high(can be looped also).The EX-OR output goes to clock inhibit (pin 13). tie all resets together and all clock pins together. Get your clock and reset with large fan-out Pin 11 will go to one i/p of self EX-OR and one i/p of next EX-OR You want them to come back and forth, then place the LEDs wherever you want. LED No.1-No.50-2-49-3-48-4-... Gajanan

12th August 2004, 11:41 AM	#14
gmphadte diyAudio Member Join Date: Jul 2003 Location: Dona paula, Goa	another ic You have to use LM339, a quad comparator with open collector. Typical output sink current is 16 mA. Connecting a currenr source instead of resistors for LEDs will save lot of wiring trouble. Connect a ladder made from LEDs to the outputs, below the cc source. Being open collector the output transistor that conducts will prevent others from lighting. Vcc--16 mA CC source--LED1 A - LED1 K----LED2 A - LED2 K----LED..... Use higher Vcc to make a longer chain K-cathode A-anode * Comparator o/p goes here Ground is not connected Gajanan

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11th August 2004, 09:41 PM	#11
cpemma diyAudio Member Join Date: Jul 2003 Location: S Yorkshire OK	For bar mode only, I'd think a raft of quad opamps (LM324) or comparators (LM339) would work out far cheaper than using several LM3914 chips. You could run the chips off say 18V and chop say a regulated 15V up with a resistor chain to use as the references for each level. A pot on the supply gives you the comparison voltage.

12th August 2004, 07:15 AM	#13
imix500 Proud Union Member diyAudio Member Join Date: Mar 2004 Location: Nashville, TN	Hi gmphadte, i see you've found the other thread. To Moderators: I didn't mean to start two threads on the same subject- my appologies. cpemma, that's another great idea. Would a LM324 or something similar be ok with outputting dc? Would it be stable driving a load such as an led? I've never used one for anything other than audio. The 3914's are under $2 each and they include everything I'd need to have a working display, but the op amp idea is interesting- might be easier to configure for custom trigger levels. Hmmm.

13th August 2004, 02:41 PM	#16
imix500 Proud Union Member diyAudio Member Join Date: Mar 2004 Location: Nashville, TN	Gotcha. That's a pretty cool idea. I'm gonna breadboard a few of these and see how they do. Thanks!