20 LED Chaser

Hi Ian,

The transistors act as "and gates". That is, they need a clock pulse at the collector AND a positive on the base to provide clock pulses to the 4017's.

The diagram at the TI (figure 19) site shows "and gates" connected between the 4017's to gate the clock pulse to the next 4017 at the proper time.

You can read about the "and gate" at

I used transistors instead of an IC for the ands, figuring it might be easier for you to get them.

By the way, building both circuits is a good idea - the more ways you have to do something, the better off you are.

Ed

Hi Ian,

You could use a transistor array chip, like the ULN2001, as the LED driver to drive 7 LEDs (or fewer) per chip. Or you could use individual NPN transistors. The output from the 4017 would connect to the input of the chip or the base of the transistor through a resistor. You need to calculate the cathode resistor for higher current if you don't use the high efficiency LEDs. The formula is: R = (Vs-Vf)/Iled where Vs is the supply voltage, Vf is the forward voltage spec of the LED and Iled is the current you want.

Ed

It shouldn't. According to the data sheet, the 4017 has about .36 mA Ioh.

You need a bank of inverters, transistors, or FETs to drive the LEDs.

Hope This Helps! Rich

There is a circuit for chasing 18 LEDs at :

Or, you can chase up to 100 LEDs using a couple decade counters and additional transistors for each LED.

-Bill

:

Correction. That should have been 1 transistor for each row and column. In other words, if you assemble the matrix with 4 rows and 5 columns to control 20 LEDs, you need 9 transistors to drive the rows and columns. The reset line of each counter needs to be connected to the appropriate output pin for the desired total. The schematic shows

25 LEDs, but can be expanded to 100. See the text for more details.

-Bill

Pretty much any sort of diode is fine there (1N914 or 1N4148 are good choices, or any rectifier diode) the purpose of the diode is to protect the unlit LEDs from reverse voltage which (if it's more than 5V) may damage them.

Some LEDS (in my experiencee) are not damaged by by upto 12 volts reverse bias, but some are damaged by less (the documentation often says 5V is the most to allow, and I've seen one damaged by 6V) small diodes are cheap and only 2 areneeded.

At any one time (without the diodes) 9 of the LEDS would be exposed to reverse voltage and 10 of them to (near) zero voltage and one of them to forwards voltage. With the diodes the 9 will get near zero too.

I'd use a polyester. For slow circuits like this the type of capacitor is not critical.

Bye. Jasen

That might be true at extreme heat (257 degrees F), but at normal temperatures the 4017 can source several mA and drive LEDs directly. If you want a 4017 to drive a LED to its max current rating, you have to use a high efficiency LED, or use one of the driver circuits you mentioned to drive a "regular" LED. The 4017 as wired in the schematic at the posted url will work fine without drivers, providing enough current to the LEDs for them to glow brightly.

Ed

one way is to use transistors and flip all the LEDs.

the bottom end use NPN transistors with 3.3K resistors from the 4017 to the base and the emiters connected to ground (battery negative). (you'll need 10) for

20mA LEDs (or even 60ma) something like BC547B or PN2222 would be suitable. if you want to use high power leds the use a darlington transistor like BD682 the top end use a 3.3K resistor from the 4047 outputs (pin 10 and 11) to the base of a PNP transistor BC337 or 2n2907, the emitters of these two got to battery positive trans and the collectors go to resistorc chosen for the apropritate LED current (470 ohms if you want about 18mA through the LEDS) then these transistors go to the LED anodes (10 leds each),

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Bye.
   Jasen

that bit with the 4011 looks unusual try instead the arrangement used by John in the top left corner of his circuit. (that part will work with the 4011 chip too)

Bye. Jasen

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Here\'s a brute force one over on abse that\'s _guaranteed_ to work:

news:59hpg454qhuls80gbombs7l8jf9lchkd9l@4ax.com

JF

Thanks. I've got more circuits than I can shake a stick at now :-)

I'm just printing them all off and still haven't managed to get all the components for one complete circuit yet! Should have the bits for one of the high eff LED circuits tomorrow.

Btw, I saw the pic of your recreation room on abse. A computer, pool table, guitar and a cat - what more could one ask for! :-)

Regards Ian

Got your circuit on abse thanks. The BC337 is an NPN transistor according to my catalog - do you mean BC327?

Regards Ian

Thanks. Jasen has posted an individual transistor style circuit which looks good and John posted a 4xIC 74 series IC circuit which looks interesting. So that's 2 more to get on the breadboard :-)

Regards Ian

Hi John. Is pin 11 of U1 supposed to go anywhere, only it's not connected in the diagram and the circuit doesn't work.

Thanks Ian