hello,
i need a help for switching a counter of 9V, which consume 50-90 mA(there are 7 segments which variate the current...
i would like to cut off this one when it pulse low(overflow of the same divice, open collector output of bc547, the output is 100mA @ 30V).
i tried to switch it with 2n3904, but it doesn't work...

(i connected the collector with the divice, the divice to the power supply, the base with the 1.2k resistor...
and the output of divice was pulled up with resistor of 1.2k, being connected to same power supply.)

i don't know if i should change the npn, or the resistors, of the connection...
please help !!

thanks a lot!!

 

i connected the collector with the divice, the divice to the power supply, the base with the 1.2k resistor...
and the output of divice was pulled up with resistor of 1.2k, being connected to same power supply.)

A schematic of this would help a lot, but from your description it sounds like the transistor base voltage could never be pulled low to turn off the device.

 

thanks so much for the answer, and you are right, i can't cut off this counter...
i attached the schematic as you say, i'm sorry for not doing this before...

i tried the V1 10.5, and 1k for each R1 and R2,
but it didn't work, so i changed the resistors for 5k, 10k, but i had the same results.
then i tried to change the V1 with 9V, 7.5V, 6V, 4.5V - and in 4.5V, it turns off when the signal is 0. (i didn't tried with the overflow yet, i've just connected the signal with the ground...)

thank you again !

 

A fundamental problem here is what the counter output will do when power is removed. The open collector output will probably not remain open, and so the steady state might be some intermediate level of being "on", or it might oscillate from on to off. I don't think there's a solution. In general, a device cannot be used to control its own power.

 

ok, i understand the problem...

i have another idea, i attached the schematic...
since it cut off when the V1 was 4.5, i wonder if it could work, if i put the pull-up voltage V2 less than 5V...?


or, is there a way to turn off this a little moment ?
even though it turns on again just after of the cut off, that will be ok for me...

for the information, this counter is composed of two parts of 4 digits, one which have a clack and another one which just count. they are connected so that they can count down maximum 99999999 seconds.



thanks a lot for your help!

 

That's still trying to control a device based on it's own output.

What are you really trying to do? Someone here can likely give a better strategy.

One thing that comes to mind is a 555-timer based monostable multivibrator circuit ("one-shot") to control power to your device. It would trigger on a negative going pulse from your counter, and turn the counter off for an adjustable period of time, and then turn the power back on. Once the cycle was triggered, the state of the counter's output wouldn't matter anymore.

 

actually i'm in a art project, that's why this counter looks like having no utility...

there are 10 down-counters, each has its own time to go(less than 99999999 seconds),
and when they get 00000000, i would like them to stay in 00000000(of turn off) ; however they stop and regain the presetted value(when the overflow pulse low in reset..) that's why i'm trying to cut off a little moment at least, so that the counters show the 00000000 at the end of their counting.. and this will prevent them from being restarted also.

today i tried to change the value of resistors in the first schematic, and i could have the 00000000 sometimes... with the R1=10k and R2=100k it seems work, but not everytime... so i would like to try to the way with 555-timer tomorrow, but i don't have the schematic of that... the exhibition will begin in a week, so if it's complicate to do, i may not be able to trying this...

in any way, i really really apreciate your help, even until now, thank you very much !!

 

... i would like them to stay in 00000000(of turn off) ; however they stop and regain the presetted value(when the overflow pulse low in reset..) that's why i'm trying to cut off a little moment at least, so that the counters show the 00000000 at the end of their counting...

Gosh, can you not control the behavior of the timer somehow, so that it does not automatically reset?

As for the schematic, just look on this site in the "Vol. VI - Experiments" link at the top of this page. More specifically, start here.

 

Gosh, can you not control the behavior of the timer somehow, so that it does not automatically reset?

if i don't reset, they will not stop counting...
i connected two kit diy, k148(clock-counter) and k154(counter), they have several programable modes, but as the 148 should count after 0000 when the k154 have more than 0000, (because the time of the 8 digits counter is left...)
and we can't stop neither k148 nor k154 during the counting except of reseting.
i attatched the datasheet of the two counters...

and thanks a lot for the advice for 555 timer, i'll study that !

 

A fundamental problem here is what the counter output will do when power is removed.

 

it does work with the 555 timer circuit as you said !!!
thank you so so much !!!!!!!!

 

Cool! It'd be nice if you posted a schematic, or even a picture, of your working circuit, to help those that might follow.

 

i used the circuit which was in the page that you linked, i replaced the R1 and D2 with the counter, and connected its output(bleu line) with B.
i put the 10.5V instead of the
it works nicely(althoug i've not yet tested to leave the counter for a long time), the counter turns off imediatly when it puls low, and turns on 3-4 seconds later.
i have a little question for this circuit, can i remouve the Rt completely? because i observed that when the Rt is cut off, the counter remain off... this result is better for me, than it returns on, but i'm not sure if it could work like this for the long time... if this will make the problems, i will put the Rt...
thanks a lot, i'm realy realy apreciate all your advice...!!!