TTL OR gate or diodes?

Archiver

Hello Stampers,

I've got two TTL level IR detectors who's logic level is inverted,
and I only have one stamp pin to work with. I'm only trying to
detect the situation when both detectors are exposed to the IR led,
meaning that there is no signal coming from either detector.

Here is the truth table:

0 + 0 = 0
0 + 1 = 1
1 + 0 = 1
1 + 1 = 1

Can I connect the TTL outputs of both the detectors to the same stamp
pin with protection diode's to prevent reverse voltage (when one is
on and the other is not). Or, do I have to put a logic chip in my
design? I'd rather not add another space consuming chip.

Thanks,
Stewart





--
Stewart Mayer, stewlist@k... on 11/19/2001

Archiver

Hi Stewart,

I would simply use 2 diodes and a resistor : each anode connected to the
output of each detector, cathode connected together and thru a 10K resistor
to the ground. That way, if one (or both) detector gives a high, one (or
two) diode is forward-biased, you get a 4.3 or 4.4 volt at the common
cathode. If both detectors give a low, then you get a low. That's it !
I think this is the simplest way to do AND functions... no chip, no power
supply.

Best regards,

Phil.

---

Original Message

---

From: "Stewart Mayer" <stewlist@k...>
Subject: [noparse][[/noparse]basicstamps] TTL OR gate or diodes?


> Hello Stampers,
>
> I've got two TTL level IR detectors who's logic level is inverted,
> and I only have one stamp pin to work with. I'm only trying to
> detect the situation when both detectors are exposed to the IR led,
> meaning that there is no signal coming from either detector.
>
> Here is the truth table:
>
> 0 + 0 = 0
> 0 + 1 = 1
> 1 + 0 = 1
> 1 + 1 = 1
>
> Can I connect the TTL outputs of both the detectors to the same stamp
> pin with protection diode's to prevent reverse voltage (when one is
> on and the other is not). Or, do I have to put a logic chip in my
> design? I'd rather not add another space consuming chip.
>
> Thanks,
> Stewart

Archiver

Thats just what I was looking for!

Thanks,
Stewart

On Mon, 19 Nov 2001 20:51:00 +0100, Philippe Derenne wrote:
>Hi Stewart,
>
>I would simply use 2 diodes and a resistor : each anode connected to
the
>output of each detector, cathode connected together and thru a 10K
resistor
>to the ground. That way, if one (or both) detector gives a high, one
(or
>two) diode is forward-biased, you get a 4.3 or 4.4 volt at the
common
>cathode. If both detectors give a low, then you get a low. That's it
!
>I think this is the simplest way to do AND functions... no chip, no
power
>supply.
>
>Best regards,
>
>Phil.
>
>
>

---

Original Message

---

>From: "Stewart Mayer" <stewlist@k...>
>Subject: [noparse][[/noparse]basicstamps] TTL OR gate or diodes?
>
>
>>Hello Stampers,
>>
>>I've got two TTL level IR detectors who's logic level is inverted,
>>and I only have one stamp pin to work with. I'm only trying to
>>detect the situation when both detectors are exposed to the IR led,
>>meaning that there is no signal coming from either detector.
>>
>>Here is the truth table:
>>
>>0 + 0 = 0
>>0 + 1 = 1
>>1 + 0 = 1
>>1 + 1 = 1
>>
>>Can I connect the TTL outputs of both the detectors to the same
stamp
>>pin with protection diode's to prevent reverse voltage (when one is
>>on and the other is not). Or, do I have to put a logic chip in my
>>design? I'd rather not add another space consuming chip.
>>
>>Thanks,
>>Stewart
>
>
>
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--
Stewart Mayer, stewlist@k... on 11/19/2001