Importance Of Pin 5 On The 555 Timer IC

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Neves
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Importance Of Pin 5 On The 555 Timer IC

Post by Neves »

I've spent a couple days trying to get an led chaser circuit and a night rider circuit to work so I can use them on my 3d printed tank to work.
I must have gone through at least 20 different Youtube channels that made these circuits and I cannot get any of them to work properly which they are all the same circuits they just change a couple of component values to make it look different. everybody copies everybody even thou it doesn't work.
In there videos they show their circuits working and I build mine carefully while watching the video's pausing and unpausing but I can't get mine to work properly for more then 3 to 5 seconds.

I fucken curse these guy's out in my head like crazy, and then I get even more angry when I go look at their circuit diagrams they posted and it doesn't match what they showed you they did on their breadboard.
None of the fucken component values match.

Anyway I did some research (cause I want to get these circuits to work) and came across this video Capacitor Function at Pin 5 NE555 | Mystery Solved!?
The video is in a different language (Read Subtitles) but he explains in great detail why pin 5 is important, he even has a working led chaser.

A capacitor (Normally a 0.01uf) needs to be connected from the Control Terminal (Pin 5) to ground of the 555 timer IC in order to:

1: Protect the IC from inadvertent application of high voltage
2: Prevent false triggering by noise coupled onto the pin
3: Convert the trigger input to sharp pulse by differentiation
$ Suppress any negative triggering pulse

As you can see a capacitor needs to be connected to pin 5 for precision applications such as a trigger for an led chaser circuit because the noise from the supply line can ride through the circuit adding small frequency noise that can cause the comparison point to vary slightly.

The 555 Timer IC Pinout

Pin 1 - Ground supply: This pin is the ground reference voltage (zero volts)

Pin 2 - Trigger: When VTRIGGER falls below 1⁄2 VCONTROL (1⁄3 VCC, except when CONTROL is driven by an external signal), OUTPUT goes to the high state and a timing interval starts. As long as TRIGGER continues to be kept at a low voltage, OUTPUT will remain in the high state.

Pin 3 - Output: This pin is a push-pull (P.P.) output that is driven to either a low state (GND) or a high state (VCC minus approximately 1.7 volts for bipolar timers, or VCC for CMOS timers).

Pin 4 - Reset: A timing interval may be reset by driving this pin to GND, but the timing does not begin again until this pin rises above approximately 0.7 volts. This pin overrides TRIGGER, which in turn overrides THRESHOLD. If this pin is not used, it should be connected to VCC to prevent electrical noise accidentally causing a reset.

Pin 5 - Control: This pin provides access to the internal voltage divider (2⁄3 VCC by default). By applying a voltage to this pin, the timing characteristics can be changed. In astable mode, this pin can be used to frequency-modulate the OUTPUT state.[16] If this pin is not used, it should be connected to a 10 nF decoupling capacitor (between this pin and GND) to ensure electrical noise doesn't affect the internal voltage divider.

Pin 6 - Threshold: When the voltage at this pin is greater than VCONTROL (2⁄3 VCC by default except when CONTROL is driven by an external signal), then the OUTPUT high state timing interval ends, causing OUTPUT to go to the low state.

Pin 7 - Discharge: This pin is an open-collector (O.C.) output for bipolar timers, or an open-drain (O.D.) output for CMOS timers. This pin can be used to discharge a capacitor when OUTPUT is low. In bistable latch and bistable inverter modes, this pin is unused, which allows it to be used as an alternate output.

Pin 8 - Positive supply: For bipolar timers, the supply voltage range is typically 4.5 to 16 volts (some are spec'ed for up to 18 volts, though most will operate as low as 3 volts). For CMOS timers, the supply voltage range is typically 2 to 15 volts (some are spec'ed for up to 18 volts, and some are spec'ed as low as 1 volt). See the supply min and max columns in the derivatives table in this article. Decoupling capacitor(s) are generally applied (between this pin and GND) as a good practice.
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