jwich asked 5 years ago
Hi Sara, Hi Rui,
having some positive results with ESP32, etc, I decided to go back to the basics once more.
From your book “Electronics for beginners” I tried several time to build this EN555 setup. Twice soldering the parts directly to a pcb board, to avoid unreliable breadboard connections and finally another try on the breadboard.
My findings:
- in the Photo you declare one resistor as 47k Ohm, in the parts list this is changed to 470k Ohm
- if you add this 47k / 470k Ohm or the 1uF or 100uF capacitor or leave any or all of them out, all three setups have a stable burning LED
- looking in the web I cannot define the difference between EN555 you recommend and the NE555P from Texas Instruments which I have bought in Germany. Is this a typo ? Actually websearch does not offer products called EN555. Conrad electronics, RS electronics and Reichelt only offer NE555 and its variants
Any idea where I went wrong or how I can test/improve my setup ?
Thanks for your reply
Jos
jwich answered 5 years ago
In the mean time I have found the solution myself:
please connect the 1k Ohm resistor from Pin 7 to plus not to ground, and the LED starts blinking. I managed to find a similar instruction for the NE555 chip. However it doesn’t need to 0.01uF mini capacitor on Pin 5.
Also I selected a 1000uF 16V Capacitor to blink once every second, anythng smaller easily blinks too fast.
Please let me know the effect of or the need for the 0.01uF capacitor on pin 5.
Kindest regards
Jos
jwich answered 5 years ago
my final setup is as follows:
pin 1: GND
pin1: minus-connector Capacitor 1000uF, then plus-connector capacitor to pin2 & Anode LED
pin 2: Anode LED
pin 3: 1K Ohm resistor to cathode LED
pin 4 & 5 : no connection
pin 6: bridge to pin 2
pin 6: 470 Ohm resistor to pin 7
pin 7: 1K Ohm resistor to pin 8
pin 8: source, anything beween 3 and 12V runs fine
in case there is a reason for using pins 4 & 5 , I would appreciate very much an explanation.After all, I wanted to go back to the basics and understand electronics …
Take care
Jos
Sara Santos Staff answered 5 years ago
Hi Jos.
I’m sorry for taking so long to get back to you.
Answering your first question.
The resistor should be 470kOhm and the capacitors are 1uF(electrolytic) and 0.01uF(ceramic).
However, other values should work too. That would change the frequency of the blinking LED.
You are right about the NE555. I don’t know why we call it EN555 in the eBook. We wrote that eBook a long time ago and I can’t remember why we call it EN555. But its name is NE555 as you mention.
Second question:
You are right about connecting the resistor to VCC and not GND. We need to correct the eBook in that diagram.
The capacitor on pin5 is to not left the pin floating. It will filter any noise that may be on the VCC power line. It will work with or without it. But if you have noise on the VCC line, it may have an unexpected behavior.
If it works fine with or without it, it’s because you probably don’t have noise.
Third question:
Pin 5 is the control voltage pin. In most circuits it is connected to GND with the capacitor (filters any noise). If you apply voltage to this pin, you can vary the width of the output signal. In our example, we’re not using it.
Pin 4 is the reset pin. It can be used to restart the 555 timer. In our case, it is connected to VCC for it to operate. If it is connected to GND, its operation is interrupted.
It may help understand if you take a look at the internal circuit of the 555 timer. Search for “555 timer internal circuit”.
I’m sorry for any typos on that eBook. It was my very first eBook and it was written a long time ago. We need to update it.
Regards,
Sara