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analog components in digital circuits

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oristim

New Member
I have been building a digital circuit with multisim 2001 and it does work fine. I am only wondering if I should add some components (capacitors and resistors) when I want to build this circuit. Can anybody help me with that? The circuit is attached in a bitmap format...
thanx
 

Roff

Well-Known Member
I suspect that your bitmap file size exceeds the board's limit. Try posting it as a .GIF or .JPG.
 

oristim

New Member
here's another try for the circuit, this time in a gif-file...
 

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  • project_1.gif
    project_1.gif
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Symon

New Member
A quick description of what you want this circuit to do would be handy....

Where were you thinking of adding these extra components?
 

Exo

Active Member
Well, it's common practice to place 100nF capacitors over the logic IC's supply lines close to every IC. For power decoupling
 

oristim

New Member
The meaning of the circuit is that I will have 1 chance out of 10 that the red lamp will light up. In all other cases the green lamp will burn. The circuit is manually switched on with a pushbutton. I used the 555 timer as driver for the top counter, which will only start to count if the bottom counter's output is 0000. The time between the swith should be enough for the top timer to count multiple times so a "random" number is generated (the top timer will stop counting if the bottom counter's output reaches 0001). While pushing on the pushbutton both timer output's will be compared and the red lamp will burn if both timers have the same output.

thanx for the help
 

oristim

New Member
I have another question, the circuit works fine with the capacitors for power decoupling exept the invertor. his output stays high, and the output of the comparator is only 2,5 volts. Does anyone know how I can solve this problem?[/list]
 

Roff

Well-Known Member
oristim said:
I have another question, the circuit works fine with the capacitors for power decoupling exept the invertor. his output stays high, and the output of the comparator is only 2,5 volts. Does anyone know how I can solve this problem?[/list]
Logic gates can't drive relays directly. You need some buffers. How much current do you relay coils draw (from the datasheet)?
 

oristim

New Member
I am using static state relays in stead of usual relays, but those are not in the database of the simulation program. I am not using the relays yet, I'm checking the outputs still with LED's because I'm still in my testfase.
I already thank you for the help.
 

Roff

Well-Known Member
oristim said:
I am using static state relays in stead of usual relays, but those are not in the database of the simulation program. I am not using the relays yet, I'm checking the outputs still with LED's because I'm still in my testfase.
I already thank you for the help.
Do you have resistors in series with your LEDs? Even with resistors, you can only get 4ma from an output and still maintain logic levels. See 74HC logic family specifications. You may need drivers for your LEDs if you want them to be bright.
 

Gandledorf

New Member
Ron H said:
oristim said:
I am using static state relays in stead of usual relays, but those are not in the database of the simulation program. I am not using the relays yet, I'm checking the outputs still with LED's because I'm still in my testfase.
I already thank you for the help.
Do you have resistors in series with your LEDs? Even with resistors, you can only get 4ma from an output and still maintain logic levels. See 74HC logic family specifications. You may need drivers for your LEDs if you want them to be bright.

Why not just have a logic gate connect to the base of a transistor, then use that to switch your other components?
 

Roff

Well-Known Member
Gandledorf said:
Ron H said:
oristim said:
I am using static state relays in stead of usual relays, but those are not in the database of the simulation program. I am not using the relays yet, I'm checking the outputs still with LED's because I'm still in my testfase.
I already thank you for the help.
Do you have resistors in series with your LEDs? Even with resistors, you can only get 4ma from an output and still maintain logic levels. See 74HC logic family specifications. You may need drivers for your LEDs if you want them to be bright.

Why not just have a logic gate connect to the base of a transistor, then use that to switch your other components?
That's generally the simplest solution. A series base resistor is a good idea.
 
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