help pls.

[sigma]

hi
i need some help troubleshooting this ckt.
i had built a prototype and seemed to work fine
but when i decided to built the actua thing it doesn,t work
am i doing something wrong?

 

[Phasor]

Without more info, we can't help you. Like when you go to the doctor and say "I'm sick", he/she can't diagnose it if you don't tell him/her the symptoms. Tell us what the symptoms of your circuit are...

 

[Phasor]

Is there an error in your schematic? It appears that one side of the relay contacts goes nowhere...

 

[bogdanfirst]

i think that the N.O. should go to where you say it is no connection...?
but still i dont get it for the display. it is a 7 segment display. why does it have n.o. and n.c. connections?

 

[Gene]

You say it dosen't work but 'we' don't know what it is supposed to do. The schematic appears to (when power is applied) light an LED, activate a relay, and light a randon segment of an digit. Maybe you were expecting something else ????

 

[Gene]

Oops - I changed my mind. The digit is receiving positive voltage from the decode IC - which makes it a common cathode type. So, if positive voltage is going to the legs of the LEDs inside the digit through the decode, where will the LEDs get the negative power? Perhaps the +5 at the top of the digit should be a (-).

 

[Chippie]

You say it dosen't work but 'we' don't know what it is supposed to do. The schematic appears to (when power is applied) light an LED, activate a relay, and light a randon segment of an digit. Maybe you were expecting something else ????

Ermm what is the 393 ?

Quad comparator feeding the bcd i/ps ?

 

[Gene]

Wow, Chippie! I totally missed the 393 tag - I assumed it was a binary decoder. Need to get an oil change and a tune-up for my glasses.

 

[Sebi]

No, i think this is 74393 = dual 7490 4bit counter...
Maybe this is light-pulse counter.I don't understand the function of relay.
Relay can never falled down, because the PNP transistor C-B resistor is 100 ohm.

 

[sigma]

ok a lot of questions to answer
1- it's suppose to be an I.R. counter. the relay is connected to the led to indicate the present state of the beam eg. broken or not.
(the N.C and N.O )
2- I've only bult the ckt half-way up to the relay to be precise
I wantedd to see if i was wiring it properly.
but the relay doesn't switch regardless of the state ot the I.R. beam.
any idea why?

 

[sigma]

oh and as for the decoder ckt.
the 393 is a 74393 and the decoder is giving a negative signal.
the 7448 gives a positive signal.

 

[Gene]

the 744x giving a + requires that the common lead of the digit be - to light the segments (you have it labeled as 5+).

I think Sebi is correct as to why the relay dosen't work.

don't give up -

 

[Sebi]

Try this...

 

[sigma]

dumb question but why r u using so many
resistors at the led. if u put just one at the +5v
it does the same thing

 

[Skyknight]

I don't think so. I don't think it's the same (it's my oppinion only). I think every LED in the 7-seg has its own circuit and needs its own resistor to control current :?

 

[Sebi]

If the display have only one resistor, the luminance of segments depend from number of activated segments.