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I am just taking a electronics course, and i am trying to understand how to build a flip flop circuit. I would like to build a circuit that has one push button, and one led. Each time the push button is pressed the state of the led would change on to off or off to on. I found this circuit http://www.josepino.com/light/led-flasher-circuits1 and i built it and it worked, but i was wondering if i could possibly adapt it to suit my purposes since it says it is similar to a flip flop. Additionally, because i am short on supplies i would like to use only transistors, resistors, capacitors, diodes, leds, and switches in the construction of the circuit. The only examples i can find online of a flip flop is a flip flop where a manual reset is necessary. I believe what i currently have is an astable multivibrator, and i think what i am trying to build is a bistable multivibrator.

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  • \$\begingroup\$ What have you tried so far? If you are taking an electronics course it would be good for you to try to figure out how the LED flasher flip-flops work. If you dive in and then have a more specific question, ask it here. \$\endgroup\$
    – Joe Hass
    Jan 6 '14 at 22:23
  • \$\begingroup\$ Note that flip flops are always "on", so they're generally not useful as a power switch. \$\endgroup\$ Jan 6 '14 at 22:26
  • \$\begingroup\$ i don't want to use it for a power switch, i am using it for a set of logic experiments \$\endgroup\$
    – popgalop
    Jan 6 '14 at 22:29
  • \$\begingroup\$ You "don't want to use it for a power switch"? Your question specifically asks about turning an LED on and off...sounds like a power switch to me! \$\endgroup\$
    – Joe Hass
    Jan 6 '14 at 22:55
  • \$\begingroup\$ But i plan as using it as a way to store one bit of information in an actual application, i am just building this test circuit as a proof of concept exercise. \$\endgroup\$
    – popgalop
    Jan 6 '14 at 23:13
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Here is a schematic for a typical T flip-flop. Every time you press the button, the output switches.

enter image description here

All you need to do is to build the logic gates! You can use diode-transistor logic, resistor-transistor logic, whatever. When you're all done, connect the inverted output (Q#) to the data pin and connect your button to the clock.

You might consider debouncing the switch. This can be achieved using a resistor and a capacitor.

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  • \$\begingroup\$ -1 From the question: "i would like to use only transistors, resistors, capacitors, diodes, leds, and switches". \$\endgroup\$
    – Joe Hass
    Jan 7 '14 at 0:39
  • \$\begingroup\$ Exactly. Those are logic gates. You build them using RTL or DTL, like I said in the answer. Drawing out every single transistor or resistor would take a really long time... Hass, did you even read the answer? Or just the first sentence and glanced at the picture? \$\endgroup\$
    – fuzzyhair2
    Jan 7 '14 at 0:40
  • \$\begingroup\$ I was looking for a circuit on a little bit of a simpler scale, however if this is the simplest way to accomplish this i will accept after i see the other answers. \$\endgroup\$
    – popgalop
    Jan 7 '14 at 0:53
  • \$\begingroup\$ I read your answer carefully, and I felt that you could just as easily drawn a microcontroller with a button and said "all you need to do is build a microcontroller". I feel that your answer was inappropriate given the obvious background level of the OP and the OP's interest in transistor-level circuits. By the way, given the OP's inexperience you should mention the need for a pulldown resistor on the switch...or is that also left as an exercise for the reader? \$\endgroup\$
    – Joe Hass
    Jan 7 '14 at 1:00
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    \$\begingroup\$ C'mon, transistor logic is even more basic than mocrocontrollers, other ICs, etc. \$\endgroup\$
    – fuzzyhair2
    Jan 7 '14 at 1:06
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DTL flip flop

This is a flip flop I designed. It is a dtl flip flop. 1 button and 2 button versions. Here is a link to my projects. this flip flop was cropped out of my 3 channel amp page. https://hackaday.io/projects/hacker/1205951 Alan Cyr

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