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my hef 4047bp monostable refuses to work

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gnosis

New Member
is there a secret to getting this chip to work?
ive connected it in retriggerable mode according to the data sheet
but the output is permanently high.
the chip is brand new and the voltage across the timing capacitor and resistor is climbing and dropping so its not dead.
whats the secret?
 

mneary

New Member
My data sheet (Document no DS005969 from Fairchild) has no diagram. Maybe you should tell us how you hooked it up.
 

gnosis

New Member
pins 4 and 14to 5volts positive
5,6,7,9,to zero volts
8,12,to positive going 2 millisec trigg pulse
2.2 meg resistor between 2 and 3
0.47 microfarad capacitor between 1and 3
output from pin 10
trigger pulse comes from radio control receiver every 20 millisecs
thanks for taking an interest
 

mneary

New Member
If the pulse comes before the end of the timer (2.5 seconds) it will retrigger (i.e. never time out).

Pin 10 will only go low if there is no pulse for more than 2.5 seconds.
 

gnosis

New Member
thanks for your reply,
sorry,but it was a bit late,i've misled you.
as you said,the output should be high with the receiver pulses triggering it
but when i simulated a receiver failure by removing the wire feeding the pulses
from the receiver ,the output remained high. i had a resistor 100k from trigger
pin down to zero volts so surely the output should have dropped?
i need that drop to enable a second receiver to take over should the first one fail.i've never used the 4047 before, i chose it because it's retriggerable
and i think if the receiver output 'jammed' in the high position it would still time out or am i wrong on that one?
the timing period of 2.5 seconds was to try the chip out so my meter could follow it . about 50 milliseconds would be needed in actual use.
maybe i should try another chip?
 
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