LED chaser/running circuit

Hobbit 77 · Post by **Hobbit 77** » Tue Mar 27, 2012 10:49 pm

I have a simple 10 LED chaser circuit that I just put together. Would like to try and make not just one LED light up and go out as it moves along the row of LEDs but instead would like to have a group of 3 or 4 LEDs light up and go out moving along the line with variable speeds. Is this possible with a circuit with a 555 and 4017 chip?

Sparky · Post by **Sparky** » Thu Apr 05, 2012 3:54 am

sounds like you are talking about dividing up the display into quadrants (well if it where a circle and you wanted 4 off LEDs at a time). When you do this you can get away with one 4017 and 555 but you may start to max out the 4017 drive circuits.

Here's an example. If you want 3 LEDs off/walking through the row, you will have 3 sets of LEDs per bank. Divide the line into 3rds.

LED1a LED2a LED3a | LED1b LED2b LED3b | LED1c LED2c LED3c

wire LED1's to output 0 of the counter
wire LED2's to output 1 of the counter
wire LED3's to output 2 of the counter
wire counter 3 output to the reset line

To help the 4017 over come the power draw of 3 LEDs per output, you may want to wire each set of LEDs in series with each other.

Vcc to + LED1a - + LED1b - + LED1c - to counter output 0
Vcc to + LED2a - + LED2b - + LED2c - to counter output 1
Vcc to + LED3a - + LED3b - + LED3c - to counter output 2

if the LEDs want 3.3 volts each, you will need Vcc to be 9.9 volts (probably a 9 volt power supply will do)

Also the 4017 will be current limiting due to its internal current handling limits. Consider that this mode has 2 outputs passing current at the any given time rather than the normal count mode of one out on at a time.

Bumping up the 3 banks of LEDs to 4 (12 total) puts your power supply needs right at 12.12 volts (for series wired LEDs). Which will work out well for 12 volt regulated supplies. No resistors needed (remember the 4017 can't really putout enough current to kill your LED strings).

Sparky · Post by **Sparky** » Thu Apr 05, 2012 4:00 am

also you won't be able to have different speeds for each bank of LEDs, as you may have guessed. They will all clock at the same time

To have [individually] varied speeds you will need a 4017 and 555 timer for each bank of LEDs.

Hobbit 77 · Post by **Hobbit 77** » Thu Apr 05, 2012 11:18 pm

Would like to be able to adjust the speed on the LEDs. Are there any schematics or project circuit kits that will create this effect?

Sparky · Post by **Sparky** » Sat Apr 07, 2012 6:09 am

I'm not sure what fx you're looking for.
1) all LED banks moving/clocking along at the same rate, but that rate is variable
2) each LED bank moves/clocks at its own rate, allowing some sequences to restart while other banks have not yet finished.
3) advanced, each bank of LEDs can progress through their sequence at their own rate but they all wait to restart at the same time (allows catchup).

Their might be a way to do option 3) with individual 4017s that you wound need to use in option 2 with the addition of something with some logic gates (hold the chip in reset until all 4017's have reached their end count). But it will take some tinkering and thinking. Let me know if that's the FX you really want. Also it might be worth it to ask the guys that do custom micro controller programs, as this will provide the smallest foot print of components.

opal_1970 · Post by **opal_1970** » Wed May 16, 2012 4:11 am

I think what Hobbit is talking about is a potentialmeter a.k.a. a little knob that by turing increases or decreases the frequency.

I do not have a lot of experience with these but it us usually just hooking up power to one pin and ground to the other. there are a lot of HowTos out there in google that can show you how to do this.