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This is a condensed circuit used for hardware debugging purposes.

The goal of this circuit is to control the 555 timer 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 for buttons 02 and buttons 03. However, button 01 still works.

enter image description here

  • Why this is the case?
  • Why does the first circuit work and the second one not work?
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    \$\begingroup\$ Schematics please and not cartoons or artist's impressions of a breadboard. Also, what has "arbitrary signal" got to do with a 555? \$\endgroup\$
    – Andy aka
    Oct 10, 2020 at 8:25
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    \$\begingroup\$ David, 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. \$\endgroup\$
    – Transistor
    Oct 10, 2020 at 8:59
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    \$\begingroup\$ @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. \$\endgroup\$
    – JRE
    Oct 10, 2020 at 9:14
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    \$\begingroup\$ Thank you for replacing the wiring diagrams with schematic diagrams. \$\endgroup\$
    – JRE
    Oct 10, 2020 at 10:31
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    \$\begingroup\$ @DavidWisniewski I feel like all that you describe suggests that the 555 is an obstacle, not a bridge towards your goal. \$\endgroup\$
    – Marcus Müller
    Oct 10, 2020 at 13:18

2 Answers 2

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Your MCU connections to the buttons/LEDs is faulty in that each MCU output connects through a resistor to ground (shown in purple below): -

enter image description here

And, each time you press one of the buttons, it will short out the 5 volt power rail.

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The reason why only one push-button worked was due to the transistors not getting the .7V that they needed to operate. This was fixed by simply readjusting the resistor values. So that the transistors had .7V on the base terminal. The Schematic made by @ tlfong01 helped lead to this answer. This is a picture from an online recource explaining why this is the case. enter image description here

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