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Hi I'm a DIY enthusiast and I got stuck with the circuit that I designed. The counter is getting very hot from the moment It's powered up.

In my setup the 330Ohm resistors at the outputs are connected to GND via a led for each resistor. (not the relays) I omitted the resistors at the parallel in inputs, and connected these directly to GND.

Please tell me what I've done wrong. The components are soldered on a PCB that I had made by JLCPCB

enter image description here

enter image description here

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In response to the comments below:

  • The Dark mode is the default in Eagle that I use. I'm sorry if the schema is hard to read, I'll change the colors in the future. Thanks for additional image.
  • The circuit is a 6 bit binary up/down counter. It needs to count upon button pushes. The logic gates around it are there to prevent underflow and overflow.
  • The circuit will operate at a frequency between 1 and 10 Hz.
  • It's getting verry hot to the feel, right after starting up. (with zero leds on) So after a few secs I switch it off.
  • Eventually circuit will control, through driver circuitry, 6 relays and the leds. On a bread board the counter could drive the leds while counting) I did not setup the full circuit though as I it was space confined and it got messy with all those wires.

For the logic part:

  • !PE = !(UpButton & DownButton)
  • !CET = !(UpButton XOR DownButton)
  • Up = !(Q0 & Q1 & Q2 & Q3 & Q4 & Q5) & UpButton
  • Down = !(Q0 | Q1 | Q2 | Q3 | Q4 | Q5) & DownButton
  • U/!D = Up

With ! == NOT, &==AND, |==OR

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    \$\begingroup\$ I inverted the image and swapped blue for a darker blue using Irfanview.. Are your eyes sensitive to white? \$\endgroup\$ Mar 13, 2021 at 19:42
  • \$\begingroup\$ Can you give a short hint what this is supposed to do? It isn't very obvious. \$\endgroup\$
    – PMF
    Mar 13, 2021 at 20:03
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    \$\begingroup\$ @TonyStewartSunnyskyguyEE75 Thank you, that dark mode schematic was unreadable. \$\endgroup\$ Mar 13, 2021 at 20:20
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    \$\begingroup\$ 74F is not CMOS! It's FAST series Schottky TTL (bipolar logic) and it will get pretty warm in normal operation. What temperature do you mean by "hot"? if it's 60 or 70C I wouldn't worry too much. \$\endgroup\$
    – user16324
    Mar 13, 2021 at 20:23
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    \$\begingroup\$ Wow, Brian is right, that thing draws around 100mA typically, that's half a watt! \$\endgroup\$ Mar 13, 2021 at 21:13

1 Answer 1

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With no load on LEDs you get 0.5W. With load, about 160mA @ 5V.

What the heck are you doing Fast TTL to drive LEDs?

Try 74ALC CMOS at 3.3V then you won’t need big resistors as the drivers are 25 Ohms or 74HC family at 5V which has 50 Ohm drivers but runs less hot with (10mA x 50 x 6) = 300 mW so 3.3 V is much better for everything using 74ALC family only.

Also all the 555’s may be replaced with hex Schmitt inverters and diode + RC to do what you want. One-shots or clocks... Or even without inverters for a pulse with cap and Pull-up.

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  • \$\begingroup\$ @dre: also the 74F and 74ALS parts are bipolar TTL - their outputs may not work reliably with 74HC and other CMOS inputs. \$\endgroup\$ Mar 13, 2021 at 23:43
  • \$\begingroup\$ Not ALS but CMOS 74ALC’ , the same used in ATMEGA high speed , low power and 25 Ohms but much better choice than 5 V logic 74HC which is ancient. Check Vol/Iol in datasheet. \$\endgroup\$ Mar 14, 2021 at 2:57
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    \$\begingroup\$ The OP has a 74ALS11 in his schematic as well as the 74F269 - I agree he should use all CMOS parts. \$\endgroup\$ Mar 14, 2021 at 3:42
  • \$\begingroup\$ I though I can combine TTL and CMOS. The reason for the 74ALS11, is that I needed to have Q0 && Q1 &&Q2 &&Q3 &&Q4 &&Q5 which can be achieved with a triple 3-input AND gate. I could not find that in CMOS. The 555 are there to debounce push buttons \$\endgroup\$
    – dre
    Mar 14, 2021 at 10:38
  • \$\begingroup\$ I added an explanation in the text above. The counter is not for driving leds, it's going to drive driver circuits that drive leds and relays. (I see how that's confusing from just the schema that I provided) The leds I only used the leds for testing the circuit, BTW on a bread board where the counter simply counted from 0 to 255 it did mot get hot driving leds. That's with a clock frequency of aproximately 1Hz. I selected the counter not because of it's speed, but because it can count both up and down, is available aa through hole and has parallel in and out. \$\endgroup\$
    – dre
    Mar 14, 2021 at 18:11

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