As I said in the previous post I’ve wanted to build a 555 timer with transistors for a while. The 555 Contest was the perfect excuse to finally make it. Although the circuit was designed by me it has the same basic blocks that make any 555 timer, and therefore the exact same functionality in a new (and pretty odd) package.
I really hope this is not a contest rule violation.
I don’t know where the idea came from, but an electronic singing flower seemed like a nice art project. The flower is made with two 555 timer (or one big 556 perhaps?) connected to each other, one with an astable configuration and the other as monostable (a setup known as Atari Console). Instead of potentiometers I used a LDR and a pair of cables as “roots”. That way the flower reacts to light and variation in soil moisture, pretty much like any flower.
It has 8 petals, 4 of them made each timer. I put some plasticine on top of a PCB board in order to have something where I could stick the transistors to while soldering them. I used it also as a template. The outline copper wire is connected to VCC.
I made half a flower first and tested;
The I built all the other petals and put everything together
There are more pictures here and below there is a short video showing the flower “singing”
This is kind of a Hello World! post. It is my first attempt with a blog and there will be a led blinking at the end.
For some reason I am always amused by those circuits that only use transistors like this clock or this 4 bit computer. For a while I’ve been wanting to build a 555 timer using transistors but I didn’t want to make those over complicated circuits that appears in datasheets. I wanted to make a simpler circuit in which I could be able to test the different blocks separately. What blocks? These blocks;
You might have seen this kind of diagram in datasheets and other places, the figure above shows clearly the different parts that makes a 555 timer. The next step was to find the simplest circuit for each part.
For the op-amp I ended up using this circuit;
All the PNP transistors are BC558 and the NPN are BC548. Testing the comparator it’s easy. I used this simple circuit that appears below and you only need a multimeter and a power supply to do so. The output is around 0,4 volts when you have less than Vcc/2 (2,5 [V]) on the non-inverting input. If you move the potentiometer slightly above 2,5 volts the output voltage sharply transition up to Vdd.
Then it was time for the logic gates. I found a couple of circuits here;
Once again testing these circuits it’s trivial, just hook up a multimeter to the output (you could use a led) and connect the inputs to “0” (GND) and “1” (VCC) and check the truth tables of the differents gates.
This is how the final circuit looks after connecting all the circuits together
There are more pictures here. And finally a short video showing both basic configurations: Astable and Monostable.