timer

[danielsmusic]

i need to make a timer for a robot im making.
if i press a button it will turn a led on for the exact same time for when i pressed the button, when i press another button the led will turn on i cannot use pic chips.

i hope i worded this one right .

thanks

 

[audioguru]

You press a button to light the LED or you press another button to light the LED.
Why use two buttons to do the same thing? :?: :?:
What activates a timer? :?: :?:

 

[danielsmusic]

i hold a button in.
i let go.
i press a other button.
a led comes on for exactly the same time i pressed the first button

 

[ljcox]

I suggest that you charge a capacitor from a constanr current source while the first button is pressed.

Then when the second button is pressed, turn the LED on and discharge the cap with a negative current source of the same amplitude. Use a voltage comparitor to detect when the cap voltage has fallen to its initial value - which will take about the same time as the charging time. When the comparitor detects the initial voltage, it turns the LED off.

Len

 

[danielsmusic]

is there a more simple way to do it :?:

do you have any drawings :?:

thanks for the idea :wink:

 

[ljcox]

I have thought about your timer.

A counter solution would be simpler. What voltage do you want to operate it from? What is the maximum time you want to hold the button for?

Do you want to hold the second button while the LED is on, ie. hold the button until the LED goes out? Or do you want it to be a momentry action only?

If you answer these questions, I'll post a suggestion for you tomorrow.

Len

 

[danielsmusic]

hold a button in.
i let go.
i press a other button.
a led comes on for exactly the same time i pressed the first button

the second button is a microswich it does'nt matter if i press it in to turn on or let go.

the only time the led should turn on is when i have let go or pressed the second button :lol:

 

[mohandessina]

Hi

I have an idea for you but i don't no if it's usefull in your situation.
anyway i suggect you to use a conter (such az 74160) to count upward while you are holding first button then count downward while you hold secend botten.
LED whil be on until you reach 0000.
using faster pulser az clock pulse will increase the timer precise.

 

[ljcox]

the second button is a microswich it does'nt matter if i press it in to turn on or let go.

the only time the led should turn on is when i have let go or pressed the second button :lol:

You did not answer all of my questions. So I have attached my suggestion without specifying Vcc and some resistor values.

When A is pressed, the counters count up. When A is released, counters stop. If B is pressed briefly, the LED is turned on and the counters count down until they reach 0000 0000 at which point they stop counting and the LED goes out.

Edit, I deleted the circuit and posted a revised one below.

Len

 

[danielsmusic]

thank! its not quite what i want but it will do.

 

[ljcox]

Here is a revised circuit.

I forgot to include a low pass filter on Co to prevent decoding spikes from resetting the flip flop.

Len

 

[ljcox]

thank! its not quite what i want but it will do.

I asked you to specify what you wanted, but your answer

the second button is a microswich it does'nt matter if i press it in to turn on or let go.

the only time the led should turn on is when i have let go or pressed the second button

is vague and ambiguous.

If you want people to do designs for you, you must specify your requirement clearly.

Len