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555 timer

Using transistors to control an astable 555 timer

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This is a condensed circuit used for hardware debugging purposes.

The goal of this circuit is to control an arbitrary signal source with only three pushbuttons. I am using the 555 timer and resistors to simulate the signal source I will be using. This is not a high-powered system therefore I do not see the need to use relays.

When the button is pushed the microcontroller will receive a digital signal to turn on the LED. At the same time, this push button will be used to allow the 555 timer to produce the desired frequency. On a fundamental level, it is combining a simple push-button circuit with the 555 timer piano circuit only difference is that these buttons need to be shared.

To start I got all of the pushbuttons working with the Arduino. Then I connected one transistor to the 555 timers and the capacitor charged and discharged appropriately to give the desired frequency.

When I connected the other transistors shown in the circuit below, the capacitor charges but it does not fully discharge to create the signal. 

  • Why this is the case?
  • Why does the first circuit work and the second one not work?

transistorsshareedit  follow  flagedited 18 secs agoasked 2 hours agoDavid Wisniewski10133 bronze badges New contributor

  • 4Schematics please and not cartoons or artist’s impressions of a breadboard. Also, what has “arbitrary signal” got to do with a 555? – Andy aka 1 hour ago
  • So you are making a NE555 astable. You pictures are too small to see clearly. Can you show us a schematic, indicating which R1, R2, C1 values you are using to fix the frequency of the oscillator? – tlfong01 1 hour ago   
  • Or you might like to refer to my NE555 astable circuit and let me know if it is similar to yours and the values you are using for your R1, R2, and C1: i.imgur.com/oEyZowH.jpeg. – tlfong01 1 hour ago   
  • 1I will update the question accordingly – David Wisniewski 1 hour ago
  • 2David, most of those wiring diagram generators can export a schematic which will need some tidy up to make it readable. You can make one by using the CircuitLab button on the editor toolbar. Double-click a component to edit its properties. ‘R’ = rotate, ‘H’ = horizontal flip. ‘V’ = vertical flip. Note that when you use the CircuitLab button on the editor toolbar and “Save and Insert” on the editor an editable schematic is saved in your post. That makes it easy for us to copy and edit in our answers. You don’t need a CircuitLab account, no screengrabs, no image uploads, no background grid. – Transistor 1 hour ago
  • 1@DavidWisniewski: What you have posted are wiring diagrams. They are used to show how to assemble a circuit. Schematic diagrams show the functional aspects of the circuit. As it stands, anyone who wants to help you first has to translate your wiring diagram to a schematic diagram. It is better if you provide the schematic. You are asking for help, so it is in your interest to make it easy for others to help. Also, you have the circuit already in a design program. It should be pretty straight forward for you to generate a schematic from your existing file. – JRE 1 hour ago

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