Hi all,
I'm having trouble with this circuit and need some insights. It's configured as an oscillator, but does not behave correctly under certain conditions. Power is applied to pin 8 (+12VDC) at all times. The circuit is activated by switch closure (actually a Darlington) which completes a ground loop to pin 1.
When a NE555P chip is installed in this circuit, it behaves normally. When pin 1 is grounded, the 555 immediately goes high (~10VDC) for ~0.5 secs and goes low for the time set per the 100K trimpot. This cycle repeats until the ground connection to pin 1 is removed.
When a MC1455 chip is installed and power applied, the pin 3 output immediately goes high (~10VDC) without pin 1 being grounded. When pin 1 is grounded, the 555 goes low for the time set per the 100K trimpot, and does not oscillate. When the time runs out, the pin 3 output again goes high.
The diodes in this circuit are both 1N4148's.
Does anyone have an idea as to why this is happening? All advice is appreciated. Thanks!
I'm having trouble with this circuit and need some insights. It's configured as an oscillator, but does not behave correctly under certain conditions. Power is applied to pin 8 (+12VDC) at all times. The circuit is activated by switch closure (actually a Darlington) which completes a ground loop to pin 1.
When a NE555P chip is installed in this circuit, it behaves normally. When pin 1 is grounded, the 555 immediately goes high (~10VDC) for ~0.5 secs and goes low for the time set per the 100K trimpot. This cycle repeats until the ground connection to pin 1 is removed.
When a MC1455 chip is installed and power applied, the pin 3 output immediately goes high (~10VDC) without pin 1 being grounded. When pin 1 is grounded, the 555 goes low for the time set per the 100K trimpot, and does not oscillate. When the time runs out, the pin 3 output again goes high.
The diodes in this circuit are both 1N4148's.
Does anyone have an idea as to why this is happening? All advice is appreciated. Thanks!
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