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Questions on 555 timers

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Jokenda

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I am working on a project where I need a delay between switching polarities on a motor when reversing direction. The carriage needs to stop, perform a specific function, then return to original starting position.

The motor will be used in 2 different circuits of opposite polarities and voltages. the seperate voltages are for controlling the speed of the carriage. I realize that I will need a delay so that first circuit can shut down before second circuit energizes.

My question is, "Can a 555 timer be used in this application or is there a chip that would be better suited?"

I have not been in electronics since 1974 and I am very rusty. A 555 timer was the neat gizmo back in the day but I have never had a use for the chip as I do today.

Any help that can be supplied would be appreciated. BTW please keep it simple, I am very rusty and not as bright or fast as I used to be.

Thank you,
John Kendall
 
The 555 is still a pretty neat gizmo. It's not used as much today because of shrinking electronic geometries, but remains a decent way to get a delay when needing to wire up something quick and dirty.
 
There is also the CMOS version which is the 7555 which draws less current in the quescent state.

You can also use CMOS Schmitt Triggers such as the 74C14, 40106, etc. which consume < 1 uA in the quescent state. But they have a wider spread of threshold voltages than the 555s. This means that you may need a trim pot to trim the timing since there will be more spread in the calculated delays than with the 555s.

However, you may need a trimpot with the 555s also since they do have some spread. Also, the resistors and capacitors used for the timing have a spead, particularily electrolytic capacitors.

Attached is an example of a Schmitt Trigger delay.
 

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Where did you get this rubbish from:

I suggest that you check the facts before you make such arrogant statements.

The data sheet I have for the 555 gives the upper threshold spread at 15 Volt @ 25C as 9.4 10.0 10.6 Volt

The DS for the 74C14 & 40106 states at 15 Volt @ 25C the + threshold spread is 9.0. 10.0 12.9 Volt

When I went to school, this is a wider spread.
 
Thankyou very much for the information! I do hope I have not started an argument as this will confuse me and I am easily confused. I have had several strokes that limit my understanding and variance from subject matter only distracts me.
Thank you,
John Kendall
 
John,
There is no argument.

The data sheets clearly show that the CMOS Schmitt Trigger ICs have a wider spread than the 555.

Here is a copy from the 74C14 data sheet

VT+ Positive Going Threshold Voltage
VCC = 15V
min = 9.0 typ = 10.0 max = 12.9 V
Spread = 12.9 - 9.0 = 3.9

VT- Negative Going Threshold Voltage
VCC = 15V
min = 2.1 typ = 5.0 max = 6.0 V
Spread = 6.0 - 2.1 = 3.9

And this is from the 555 DS

VTH Threshold voltage
VCC=15V
min = 9.4 typ = 10.0 max = 10.6 V
Spread = 10.6 - 9.4 = 1.2

VTRIG Trigger voltage
VCC=15V
min = 4.8 typ = 5.0 max = 5.2 V
Spread = 5.2 - 4.8 = 0.4

As you can see, I've calculated the spreads & posted them in red.

The 555 has significantly less spread than the 74C14.
 
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