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aromph

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I am building a ckt that would alarm when the input is high using 74ls32 OR gate. Someone advised me to use 74ls33 NOR gate because it has an open collector output, which according to him is better than 74ls32.

I wanted to know the difference between an open collector output with that of not an open collector output. I have no problem using NOR or OR gate.

What is difference in stability, response, current consumption, voltage capacity? or whatever you can share.

Thanks!

Open collector outputs does not have internal pull-ups. Using open collector outputs your input and output voltages can be different. That means you can operate your NOR gate using TTL levels (0-5V) while you have freedom to operate your output load (connected between +V and NOR gates output. +V is another supply say 12V) voltage other than TTL levels. In this case it is 12V. So you can directly drive a Piezo buzzer through NOR gates output without using additional transistor at the output.

The 74LS33 datasheet says the maximum voltage on the output (with both inputs low) is 7 volts. It can sink 24ma.
The 74LS26 is an open collector NAND buffer that can handle 15 volts, but it can only sink 8ma, and you would have to invert your input levels.
If you are using a NOR gate, you must have more than one input. How many do you have? Does each input go high (independently) when the alarm needs to sound? How much voltage and current does your alarm require?

kinjalgp said:
Open collector outputs does not have internal pull-ups. Using open collector outputs your input and output voltages can be different. That means you can operate your NOR gate using TTL levels (0-5V) while you have freedom to operate your output load (connected between +V and NOR gates output. +V is another supply say 12V) voltage other than TTL levels. In this case it is 12V. So you can directly drive a Piezo buzzer through NOR gates output without using additional transistor at the output.

Thanks for the reply, I do understand based on your explanation that I can directly drive my output load, which in this case, is a piezo buzzer without using a transistor but I don't understand how am I going to connect my output load between +V and NOR gates output. Considering, what if my NOR gate output goes high and my output load is connected to +V and NOR gate output.

If you are using a NOR gate, you must have more than one input. How many do you have? Does each input go high (independently) when the alarm needs to sound? How much voltage and current does your alarm require?[/quote]

Thanks Ron H for the reply,

I will be using multiple inputs.
Each input will go high independently, the output is supposed to trigger an alarm whenever there is a high input.
I am still on the thinking stage of what type of alarm will i be using.
I am considering a low voltage, if I may, I would like to use the supply voltage of the circuit which in this case is 5 volts or lower. as long as it triggers whenever or any of the input goes high.

aromph said:
kinjalgp said:
Open collector outputs does not have internal pull-ups. Using open collector outputs your input and output voltages can be different. That means you can operate your NOR gate using TTL levels (0-5V) while you have freedom to operate your output load (connected between +V and NOR gates output. +V is another supply say 12V) voltage other than TTL levels. In this case it is 12V. So you can directly drive a Piezo buzzer through NOR gates output without using additional transistor at the output.

Thanks for the reply, I do understand based on your explanation that I can directly drive my output load, which in this case, is a piezo buzzer without using a transistor but I don't understand how am I going to connect my output load between +V and NOR gates output. Considering, what if my NOR gate output goes high and my output load is connected to +V and NOR gate output.
A NOR gate output is only high when all inputs are low. This is when you want your alarm to be off. If any input goes high, the output goes low, applying 5 volts across your alarm.

This is how you use Open Collector OR gate with 12V load supply voltage.
NOR gate is also used in same way.

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• nor.gif
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To Ron H and kinjalgp:

Thanks to both of you..... I'll try these on my circuit, till next time.....

Gracias!

I didn' get the idea of the circuit you draw, kinjalgp. Is that an open collector? I thought open collectors were just connecting outputs of many gates together and having a load resistance in the end, or something like that...

Keep in mind that 12 volts may damage a 74LS33. Below is a 2-input NOR that is very simple.

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• nor_147.gif
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Agent 009 said:
I didn' get the idea of the circuit you draw, kinjalgp. Is that an open collector? I thought open collectors were just connecting outputs of many gates together and having a load resistance in the end, or something like that...
Yes that is an open collector OR gate. Open collectors does not have internal pull-ups so you need to connect them externally.

Ron H said:
Keep in mind that 12 volts may damage a 74LS33. Below is a 2-input NOR that is very simple.

Thanks again Roh H! I still have a question. If the description of the 74LS33 that I have says it's open collector output rated 35Volts dc, does this mean that there is still a possibility that it may be damaged?

I also would like to make the tone of the buzzer pulsating once triggered ( say, 10ms ), What can I add to the circuit?

For pulsating buzzer, you could use 555 astable multvibrator whose output is ANDed with your alarm signal.

The other simpler method is to use a Buzzer with in-built pulsating tone circuitry. It is cheaper and easy to procure.

kinjalgp said:
For pulsating buzzer, you could use 555 astable multvibrator whose output is ANDed with your alarm signal.

The other simpler method is to use a Buzzer with in-built pulsating tone circuitry. It is cheaper and easy to procure.

Thanks kinjalgp! and how do i connect ( ANDed with the alarm signal? )can you help me with the drawing, you see i'm having hard time trying to buy this pulsating buzzer.

This is how it is done.

If your AND is open collector, then you can directly connect Buzzer at its output. Or use transistor to drive the buzzer. Use CMOS version of 555 i.e. 7555.

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• Alarm.gif
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aromph said:
Ron H said:
Keep in mind that 12 volts may damage a 74LS33. Below is a 2-input NOR that is very simple.

Thanks again Roh H! I still have a question. If the description of the 74LS33 that I have says it's open collector output rated 35Volts dc, does this mean that there is still a possibility that it may be damaged?

I also would like to make the tone of the buzzer pulsating once triggered ( say, 10ms ), What can I add to the circuit?
Who makes the 74LS33 that you have?

Thank you so much kinjalgp!

You're great!

Who makes the 74LS33 that you have?[/quote]

I think it's ECG ( Philips I guess ) am not really sure.
Thanks anyway for the response.

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