decoupler question

Mikebits said:

A pull up is a resistor that tends to pull a line towards a positive level as in +v. A pull down attempts to pull a line towards ground level. The choice of a pull up or pull down is often selected based on many factors. Some are, open collector outputs, or if line may go tri-state, or the driver needs help sourcing or sinking current, these are but a few reasons.

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hi, could you elaborate on this 'open collector outputs'? i'm confused with sourcing and sinking current and never able to comprehend the application and the interface. hope to get some advice. Thanks

i read some stuff about decoupling, this is the closest i had found:

https://www.logicdevices.com/support/appnotes/lf44xx_appnote_decoupling.PDF

i'll get back at this tomorrow, good night thanks guys

snooze said:

hi, could you elaborate on this 'open collector outputs'? i'm confused with sourcing and sinking current and never able to comprehend the application and the interface. hope to get some advice. Thanks

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hi,
Open collector or open drain outputs are where there is no 'internal' resistor attached to the collector or drain.

This means that the user needs to add an external load connected to the collector or drain, the external load can be a resistor or a relay for example.

On some devices with open outputs the open collector/drain can have a higher voltage rating than the remainder of the device.

An example would be the 74LS07 ic, where the supply voltage to the ic is +5V/0V but the open collector transistor is rated at +30V max.

A 'sink' is usually where the transistor is connected in the 'low' side of the load and when switched ON connects the load to 0V. An open collector transistor is a sink when used in this way.
A ULN2308A is an example of a 'sink'

A 'source' is usually where the transistor is connected in the 'high' side of the load and when switched ON connects the load to the +V supply.
A ULN2981 is an example of a 'source'

Get the datasheets from Datasheet Archive - Free Datasheet Search Engine - PDF Datasheets - Data Sheet - Datasheet - Application Note - Free Texas Instruments Samples for these last two devices and you will easily follow source/sinking...

ericgibbs, Thanks for the explanation.

ULN2308A is not available.. couldn't get the data sheets.

snooze said:

ULN2308A is not available.. couldn't get the data sheets.

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hi,
Here you go.

Thanks....

There are two supply voltages:
1) The 555 will not work when its pin 2 is only 5V but its supply is 12V.
2) The PIC will be destroyed when it has a 5V supply and has an input from a 555 that has a 12V supply.

audioguru said:

There are two supply voltages:
1) The 555 will not work when its pin 2 is only 5V but its supply is 12V.
2) The PIC will be destroyed when it has a 5V supply and has an input from a 555 that has a 12V supply.

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hi agu,
I have explained to the OP that an opto isolator and 555 timer are not required at all.!

The coin mech runs from +12V/0 and it has a simple mechanical switch that detects the passage of a coin.
The switch is powered by the +12V and gives a 30mSec pulse, the pulse only requires a 3k3,2K2 divider to provide the +5V pulse for the PIC's PORTB.0 interrupt.

yes Uncle $crooge.

i'm fortunate my pic did not blow up or something since i actually tried to connect directly the two together lol (out of stupidity). eric taught me to use the resistor divider approach and it worked out pretty well, plus i think with matching resistor-capacitor filter, i was yakking about multiple readings last time and he helped me.

thank you guys

*graciously helped me