Powering multiple LEDs via IC

Thread Starter

lotsofhobbies

Joined Feb 5, 2017
11
Hi,
The best way to describe my project is like a battery charge level status indicator. I'm using a 555 IC to a 4029 binary up/down counter to a 4028 binary decoder. There are ten LEDs connected to the ten 4028 outputs. The bit I'm struggling with is getting multiple LEDs to light simultaneously, eg. for output value 5 I want 5 LEDs to light up then for output value 6, 6 LEDs etc. I've attached a picture of two solutions I've found that work - one with LEDs in parallel, one with them in series. I prefer the parallel circuit I don't need to determine a resistor value for each combination of LEDs - also no risk of "running out" of voltage. I am powering from a 9V DC battery.

My question is whether I'm making this overly complicated? It seems I need a lot of diodes considering the LEDs are diodes themselves. Also I'm not sure if I will reach a limit as to how much current the ICs will pass through them (eg if I keep adding more LEDs) or whether that's just limited by the size of battery I use. I could use transistors to make sure I give the LEDs full power but that would be even more complicated and not sure it's required.image.jpeg

Thanks a lot for any help in clearing this up for me

Andrew
 

eetech00

Joined Jun 8, 2013
3,859
Hi,
The best way to describe my project is like a battery charge level status indicator. I'm using a 555 IC to a 4029 binary up/down counter to a 4028 binary decoder. There are ten LEDs connected to the ten 4028 outputs. The bit I'm struggling with is getting multiple LEDs to light simultaneously, eg. for output value 5 I want 5 LEDs to light up then for output value 6, 6 LEDs etc. I've attached a picture of two solutions I've found that work - one with LEDs in parallel, one with them in series. I prefer the parallel circuit I don't need to determine a resistor value for each combination of LEDs - also no risk of "running out" of voltage. I am powering from a 9V DC battery.

My question is whether I'm making this overly complicated? It seems I need a lot of diodes considering the LEDs are diodes themselves. Also I'm not sure if I will reach a limit as to how much current the ICs will pass through them (eg if I keep adding more LEDs) or whether that's just limited by the size of battery I use. I could use transistors to make sure I give the LEDs full power but that would be even more complicated and not sure it's required.View attachment 119966

Thanks a lot for any help in clearing this up for me

Andrew
Hi

You'll need comparators and LED drivers. Its easier to use a chip like an LM3914.
 

Thread Starter

lotsofhobbies

Joined Feb 5, 2017
11
Thanks everyone for your help so far. I've attached the full circuit as requested. I didn't want to overload with too much info but may have put people on the wrong track with the battery status analogy. The LEDs are simply to count up or down like a bar graph based on time (555 signal). A switch is used to determine whether to count up or down. (The LEDs should also stop once they get to 10 or 0 depending on whether counting up or down which I think I can do using pin 5 of the 4029 and an AND gate connected to the switch and output 1 and 10)

BarGraphTimer2.jpg

I had a look at the other chips mentioned - the LM3914 looks interesting although that's based on voltage change so I'm not sure I can adapt it for my circuit?

My circuit works - at least for the number of LEDs I've attached but I was mainly unsure about powering the LEDs through the IC's and just any other feedback since I'm just sort of making it up as I go. Initially I had set-up with a whole bunch of transistors to translate the binary output of the 4029 because I hadn't realised the 4028 binary decoder existed and would do that for me!

Thanks again,
Andrew
 

Bernard

Joined Aug 7, 2008
5,784
An other version, done during super bowl, so watch for errors. First- did not like the way the re-start SW came out, but forgot to add an invertor stage to make it into NOR. SW is NC SP from 555-4 to output of ( N )OR gate. A momentary push should start the count. At either 9 or 0 555-4 will go low, stopping the clock.
The OR outputs will need LED drivers. A 4049 is shown as an example, good for 10 mA @ 9 V Vdd, 6 stages,UP-DN BAR GDPH 00000.jpg or FET, or ULN2004, with 7 stages / chip.
 

Thread Starter

lotsofhobbies

Joined Feb 5, 2017
11
Bernard,
The 4071 looks great - basically simplifying my circuit by replacing the diodes with ORs. When I looked for more info on it I found there's a whole family of logic chips so that's two break throughs!
In your second example (#19) I'm not sure what you've drawn at the bottom,eg. under the 555? Also why do the LEDs need drivers rather than just connecting to the outputs?
Thanks,
Andrew
 

Bernard

Joined Aug 7, 2008
5,784
4071 low level output @ 10V = 2.25 mA, high level = .88 mA.
#9 under 555 looks like unused stages, which should have all inputs going somewhere
or they may oscillate creating noise.
Not shown on # 10 is power supply decoupling, maybe a 10uF & a .1 uF from + 9 V and ground. More ICs of the 4000 family is 74AC00.
Counter connected as BCD, but it makes no difference here as count never goes above 10.
 

Thread Starter

lotsofhobbies

Joined Feb 5, 2017
11
Oops that was supposed to be post #10 not #19 - it was the elements along the bottom just above the text UP DN BAR GRAPH and to the left that I didn't understand. Anyway I think I need to get hold of the two new chips and have a play around with it.
Thanks a lot for your help!
 

Bernard

Joined Aug 7, 2008
5,784
Still the same answer, unused inverters & ORs, showing that unused inputs must go somewhere. Also shown is power & ground connections, note strange location for Vdd
on 4049.
 

hp1729

Joined Nov 23, 2015
2,304
Hi,
The best way to describe my project is like a battery charge level status indicator. I'm using a 555 IC to a 4029 binary up/down counter to a 4028 binary decoder. There are ten LEDs connected to the ten 4028 outputs. The bit I'm struggling with is getting multiple LEDs to light simultaneously, eg. for output value 5 I want 5 LEDs to light up then for output value 6, 6 LEDs etc. I've attached a picture of two solutions I've found that work - one with LEDs in parallel, one with them in series. I prefer the parallel circuit I don't need to determine a resistor value for each combination of LEDs - also no risk of "running out" of voltage. I am powering from a 9V DC battery.

My question is whether I'm making this overly complicated? It seems I need a lot of diodes considering the LEDs are diodes themselves. Also I'm not sure if I will reach a limit as to how much current the ICs will pass through them (eg if I keep adding more LEDs) or whether that's just limited by the size of battery I use. I could use transistors to make sure I give the LEDs full power but that would be even more complicated and not sure it's required.View attachment 119966

Thanks a lot for any help in clearing this up for me

Andrew
You are pushing the current capacity of the 4028. One option is the attached. I only had room to show 5 LEDs but you can get the idea. Every output pulls all lower outputs low.
 

Attachments

Thread Starter

lotsofhobbies

Joined Feb 5, 2017
11
You are pushing the current capacity of the 4028. One option is the attached. I only had room to show 5 LEDs but you can get the idea. Every output pulls all lower outputs low.
Thanks. That looks very tidy. I've been reading about forward voltage over diodes - I think the thing that might trip me up is the voltage drop over the sequential diodes but can probably get it if I up my battery voltage to 12V.

Thanks again!
 

AnalogKid

Joined Aug 1, 2013
10,987
Back to the original question, you want a group of LEDs to step up or down like a bar graph, clocked by a 555, with direction determined by a switch? Correct?
This circuit has no connection to the battery voltage being monitored, correct?

Something you haven't mentioned before, what happens when the circuit gets to the top count? Do you want it to turn off all LEDs and start the cycle over again, like a sequential turn signal, or step the LEDs up to where they all are on and then hold until you change the direction switch?

Are 8 stages enough? If so, a bi-directional shift register will do what you want. You still will need output drivers for the LEDs, but that is true for any of these circuits using standard CMOS parts.

ak
 

Thread Starter

lotsofhobbies

Joined Feb 5, 2017
11
Back to the original question, you want a group of LEDs to step up or down like a bar graph, clocked by a 555, with direction determined by a switch? Correct?
This circuit has no connection to the battery voltage being monitored, correct?

Something you haven't mentioned before, what happens when the circuit gets to the top count? Do you want it to turn off all LEDs and start the cycle over again, like a sequential turn signal, or step the LEDs up to where they all are on and then hold until you change the direction switch?

Are 8 stages enough? If so, a bi-directional shift register will do what you want. You still will need output drivers for the LEDs, but that is true for any of these circuits using standard CMOS parts.

ak
Back to the original question, you want a group of LEDs to step up or down like a bar graph, clocked by a 555, with direction determined by a switch? Correct?
This circuit has no connection to the battery voltage being monitored, correct?

Something you haven't mentioned before, what happens when the circuit gets to the top count? Do you want it to turn off all LEDs and start the cycle over again, like a sequential turn signal, or step the LEDs up to where they all are on and then hold until you change the direction switch?

Are 8 stages enough? If so, a bi-directional shift register will do what you want. You still will need output drivers for the LEDs, but that is true for any of these circuits using standard CMOS parts.

ak
Hi. Your interpretation is correct. I've actually made quite a bit of progress with this. I made most of the circuit that Bernard drew up for me. It got pretty complicated (ran out of room on my breadboard) but I learned a lot in the process. I was interested in the diode idea from hp1729 because it would simplify things a bit.

But my current idea is to ditch the 555 and use a capacitor with a Zener diode (another new find) connected to a LM3914 as suggested right at the start (but I hadn't thought of the capacitor idea). When the capacitor is fully charged the lights will stay on until I flip the switch (which is what I want) and will then discharge till I flip the switch again. (This is for a game I'm making)

I've got the LM 3914 circuit working tonight :) and I figured out the Zener diode the night before. The capacitor time constant doesn't seem to match theory but that's probably because the multimeter was discharging it. Need some more work on that and then will post back success or a question. If it works it will be much simpler than the 555, 4029, 4028, 4073 version. And I don't think I need the LED drivers either??

Thanks. Blown away by all the help I've had with this!!
 

Thread Starter

lotsofhobbies

Joined Feb 5, 2017
11
Note that a simple R-C ramp is not linear, byt the comparator distribution inside the 3914 is.

ak
And I thought I was nearly there! I had thought it would be good enough but plugging in some numbers i see it will be hopeless- everything happening in the first 4 minutes and then practically nothing from there to 10mins.

It looks like I might be able to fix the charging current to the capacitor by using two transistors and thereby get a linear voltage increase. Haven't found a really clear circuit to demo that and I'm not sure if it will work the same way in reverse- ie. to get a linear voltage decline?

Thanks again
 
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