20 LED Chaser

There are many solutions to your request Ian. Here is one possibility:

You can also build two of the circuits you have already found and alternately enable them to accomplish your goal.

You can use cascaded 4017's to do it. See

Ed

use a 4047 wired as an astable multivibrator for the oscilator. and a 4017 decade counter, clock the 4017 from pin 10 of the 4047 use pins 10 and 11 to select between two banks of 10 LEDs.

if you use high efficiency LEDs the whole thing will run off 3v with just those two chips a resistor and a capacitor for the clock and two resistors to control brightness.

Bye. Jasen

Thanks for the link. Must admit I'm a bit of a newbie at this but the circuit diagram I have for 10 LEDS is this:

Any idea how you woudl modify that circuit to include a second cascaded

4017?

Thanks Ian

--
Yup!

news:bdmeg4hke2vgn039r3agut9dcu0npnf1hf@4ax.com

JF

Hi. Is that meant to be a link to another thread only I can't read it?

Ian

"IanW" schreef in bericht news:ge95nu$an5$ snipped-for-privacy@aioe.org...

alt.binaries.schematics.electronic

28-10-2008

petrus bitbyter

That's fantastic thanks :-)

Just a couple of questions:

- R3 (& R4) would be 330ohm as I plan to use a 9V PP3 battery and the LEDs are 2V 20mA, but do I need 1 resistor for each of the 10 LEDs connected to U2 or just the one (as in that circuit on free-circuit-diagrams.com)?

- I'm not sure I understand the bit of the schematic around C1 & R1. VCC is presumably the V+ from the battery, but where is the V- negative rail?

Thanks Ian

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Just the one, but it\'s 9 LEDs, not 10.

Matter of fact, since there\'ll only be one LED on at a time anyway, you
ought to be able to be able to connect the 18 LEDs remaining LEDs to
ground through a single resistor.

I thought it was 10 on each since the schematic shows Q0 to Q9 (presumably that's the order in which the LEDs illuminate?) and their corresponding IC pins. Should I leave one of those unconnected?

Regards Ian

--- No, just change the reference designation of LED2 to LED11, connect the cathodes of the remaining 18 LEDs to the remaining 18 outputs of U2 and U3, and connect all of their cathodes to ground through the one resistor.

BUT... there's a big problem which I just noticed, and that's that if LED1 and LED11 are operated at 20mA, then the internal CMOS voltage drops will be too great for the logic to work properly when LED1 or LED11 are on, and the whole thing will probably hang. 20mA is also too high for the rest of the outputs, so the obvious solution is to use high-efficiency LEDs. Something like an HLMP-4700 with a Vf of 1.7V at

2mA would be OK.

JF

Oops...

^^^^^^^^ anodes

JF

--
Here; on abse:

news:s7ijg4l896sq4gjajmetrkokbi2vetsk8n@4ax.com

JF

The diagram at

shows 3 4017's, not two. It uses the first 4017 to control LEDs 1 through 9, the second to control LEDs 10 through 17, and the third to control LEDS 18, 19 and 20.

I can email a jpg of the schematic for that circuit.

I will "draw" an ascii schematic below that shows the interconnections required between the 4017 ICs. It does not show the LED wiring - that wiring will be described. LED wiring is very close to what is shown at the url you posted for free circuits. You can use the 4011 clock circuit from that page.

CLOCK +-----------------------------------------------+ | | +-----------+ +-----------+ | | | | | | | | | ---15---- | ---15---- | ---15---- | | | | | | | | | | | +----14 | | +---14 | | +---14 | | | | IC1 | | | | IC2 | | | | IC3 | | | +-13 | | | +-13 | | | +-13 | | | | | | | | | | | | | | | | | | | --3--11-- | | | --3--11-- | | | ---10---- | | | | | | | | | | | | | | | | | +-- | ----+ | | +-- | ----+ | | +-------+ | | | | | | | | | | +--------+ | +--------+ | +--+--[15K]----+ | | /e | /e | | | +-[1K]-| 2N3904 +-[1K]-| Gnd [C1] | \\c Q1 Q2 \\c | | | | +9V +--------------------+-------------------+

How it works: At power on, C1 (.01uf) and the 15K resistor send a (+) reset pulse to IC1, which forces pin 3 on (+). That in turn resets IC2, which in turn resets 1C3, so all three 4017's are set to 0 upon power on. There is _no_ LED connected to pin 3 for IC2 or IC3, but there is an LED (LED1) connected to IC1 pin 3. Clock pulses are applied to IC1 pin 14 and to the collectors of both transistors. These transistors (both are

2N3904's, but you can use almost any NPN) will not pass the clock pulses through to the emitter, until the base goes positive.

With each clock pulse, IC1 advances one count, lighting LEDs 2,3,4,5,6,7,8 and 9 in sequence. The next clock pulse extinguishes LED9 and causes pin 11 to go + . That places

• on the base of Q1 and on pin 13 of IC1. With pin 13 positive, IC1 is frozen until it gets a reset pulse. With the base of Q1 +, the same clock pulse that moved IC1 causes IC2 to increment from 0 to 1 and light LED 10. (Since there is no LED connected to the count 0 pin (pin 3), IC2 must increment to 1 before it can light an LED.) IC2 is wired to LEDS 10 through

17, as mentioned earlier. It operates identically to IC1.

When IC2 places + on its pin 11, it places + on the base of Q2 and freezes as IC1 did. Because the base is +, Q2 can now pass clock pulses to IC3, and it can advance. It lights LEDs

17, 18, 19 and 20 in sequence. At the next clock pulse it places a plus on pin 10, which sends a reset pulse to IC1, and the entire operation starts over.

_LED wiring recap:_ All 20 of the LED cathodes connect to a resistor (R3 at the url you posted) - make it 3.3K and use the LEDs John recommended. LEDs 1-9 connect to IC1 as shown on the url you posted. _NO_ LED is connected to pin 11 of IC1. LEDs 10-17 connect to IC2. _NO_ LED is connected to pin 3 or pin 11 of IC2. Otherwise, the LED wiring is the same as that shown at t6he url. LEDs

18, 19 and 20 are connected to IC3 pins 2, 4 and 7 respectively.

Ed

I'll hopefully be able to get some 5mm superbright red low current LEDs locally tomorrow. The catalog (Maplin) says they draw 2mA and have a forward voltage max of 2.5V. So that should suit the 3.6K resistors at R1,3 & 4 in your new schematic.

I have actually tried assembling the circuit on that free-circuit-diagrams.com site, however it doesn't work properly. That is, the LEDs just seem to flash randomly, some flickering very very briefly and then one will stay lit for 2-3 seconds and it'll seem to lock up for a bit before randomly flashing again. I wonder if this is because of the 20mA LEDs?

Thanks for taking the time to help and explaining things :-)

Regards Ian

Hi Ed. That's a brilliant and very clear description :-).

I think I understand the function of the two types of IC but I'm not sure sure what the transistors are actually for? John's circuit doesn't feature any - is that because U1C & U1D perform a similar function?

I have some breadboard, so am going to make both yours and John's circuits and work out the component layout. Should be fun.

Thanks very much for your help Ian

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My pleasure!  :-)

I\'m not familiar with that site; do you have a link to their simulator?

JF

Sorry I should have been more specific, I meant I assembled the 10 LED chaser that I posted previously about:

and it doesn't work properly.

Regards Ian

Hi Jasen. Thanks for the schematic on abse, that looks good too and makes 3 circuits to try out :-)

I guess I might be pushing my luck here, but any suggestions for a chaser that will work regardless of the current that the LEDs require? I've mail ordered some high eff LEDs, since my local electronics supplier didn't have any in stock today, but there's more choice of size/colour/brightness with normal LEDs.

Regards Ian