trouble with logic counters

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- panfilero
  
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posted
17 years ago

Tue, Jan 2, 2007 5:05 AM

Hello, I'm trying to hook up a 74HCT163 to count from 0 to 7 then loop and keep doing it. I'm having a lot of trouble making sense of the data sheet on how to connect this thing. I have a 555 chip creating my clock, it's lighting an LED right now, I took that from the positive end of the LED and am running it into the counter. I was worried about going straight from the 555 chip to the counter cause i've heard these type of chips are fragile, real sensitive to too much current/voltage. I'm powering the circuit with a 9 Volt battery, I'm splitting that in half using a couple resistors (of equal value 10 Mohm) in series and taking the voltage from one resisttor and using it as my high for the counter. I've connected the pins in this way:

1 MR - high 2 CP - 555 output 3 P0 - high 4 P1 - high 5 P2 - high 6 P3 - high 7 PE - high 8 GND - ground 9 SPE - high 10 TE - high 11 Q3 - not used 12 Q2 - to a 1K resistor in series with an LED 13 Q1 - to a 1K resistor in series with an LED 14 Q0 - to a 1K resistor in series with an LED 15 TC - not used 16 Vcc - high

I can't get anything to happen, and can't tell what some of these pins are even for. Any help with this would be greatly appreciated, thanks

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- tersono
  
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posted
17 years ago

Tue, Jan 2, 2007 9:06 AM

Whoa- what's powered from what? Your description leaves room for confusion.

If you're running the '163 from the junction of the two 10M, then that's like feeding it from 4.5v- OK- !!!!! *but with 5M in series with the supply*!!!!!

- and even if the '163 pulls only a microamp, that leaves it with no supply volts. (Does "Thevenin" mean anything to you?)

If you've put 9v directly on the '163, you've probably broken it. (But maybe you don't mean that).

Why not run everything from 4.5v? Your LEDs would be dimmer, but live with that. Put 1n or 10n capacitor across the supply

is master reset- active low- so you're letting it run. OK

clock input to '163- OK

above are parallel data inputs- don't matter for your purposes

Count enable- OK

Low would force counter to state of pins 3...6- so OK

Enables carry input- OK

OK

-- Per ardua ad nauseam

- C
- CWatters
  
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posted
17 years ago

Wed, Jan 3, 2007 10:37 AM

That won't work...

Each output LED that is illuminated will draw a few mA in through pin 16 and out of the relevant Q of the 74HCT163. That current would cause a large voltage drop through the 10M resistor betwwen Pin 16 and the 19V battery. Lets estimate the current at 2mA - the voltage drop would be 2 x 10^-3 x 10 x 10^6 or about 20,000V or at least it would if the supply voltage was

Why not power the whole circuit from a 5V source and use version of the 555 that will work from 5V power rails. If you need to make 5V from 9V then use a three pin reglator (7805 series) and some capacitors.