Diode ORing

flyingnunrt

Senior Member
What is the best type of diode to use for ORing a few inputs to a 08M from several IR receivers, eg. Vishay TSOP2438 Type devices?
Input pulse signal will be about 500us duration, but later when 18M is released, could be 50us.
1N914 (don't have any on hand)
1N4148 (I think these will be OK & I have a couple on hand for testing)
1N1004 (not sure if these will be OK at 50us but I have a bag full of these)
other ???
 

Technical

Technical Support
Staff member
You don't need any diodes. As these IR receivers are open collector devices there is no harm in using one pull up resistor and multiple sensors on the same line.

In theory it is not a good idea as each sensor could pick up the signals out of sync and corrupt each other e.g. one receiving direct and one getting the 'bounced' signal off a wall. However in reality we have often used two sensors 'back to back' to give better coverage and it worked quite well.
 

SAborn

Senior Member
I dont see much difference between any of what you have listed except for the current they are able to handle.
I have no idea what the heck a "ORing" is except for a rubber ring used as a seal most times.

From what i can gather that you need to do, any of the diodes you list will do the same job.

There is nothing fancy about any of them, other than they are a standard silicon diode.
 

chigley

Senior Member
I dont see much difference between any of what you have listed except for the current they are able to handle.
I have no idea what the heck a "ORing" is except for a rubber ring used as a seal most times.

From what i can gather that you need to do, any of the diodes you list will do the same job.

There is nothing fancy about any of them, other than they are a standard silicon diode.
I thought this at first, then realised the OP means "OR"-ing (i.e. an OR function) not an "O"-ring :)
 

SAborn

Senior Member
Ok i follow now.
Thought we were talking plumbing there for a while.
I had kinda thought perhaps it was a check valve needed and not a diode.
 

hippy

Technical Support
Staff member
What is the best type of diode to use for ORing a few inputs to a 08M from several IR receivers, eg. Vishay TSOP2438 Type devices?
Input pulse signal will be about 500us duration, but later when 18M is released, could be 50us.
TSOP devices include a lot on top of the 'photo transistor' to detect IR; amplifier, AGC and demodulator. They need a continuous stream of IR modulated at ~38kHz to present a signal and 38kHz has a period around 26us.

The TSOP output will usually only activate some time after the stream is started and pulses are detected so you may not be able to get the IR stream period down to as short as you are hoping for. In the datasheet I found the 'Td' time in figure 1 "Output function" defines what the minimum stream present time must be and later states, "Burst length should be 10 cycles/burst or longer"; about 260us minimum.
 

Dippy

Moderator
Flyingnun, READ & HEED what hippy has said above.
It is very important.
READ the data sheet for the device you are using , then you can see the limits.

To start doing fast stuff you'll have to get all the speeds up and maybe roll your own receiver (which I suspect you won't want to do). You'll be able to get down to 10uS (unmodulated) with a TBA2800 and faster if you start experimenting with devices at the nitty-gritty level.
 

Minifig666

Senior Member
You have to be careful with diode logic, sometimes the gates don't do exactly what you expect. You should be OK with an OR gate (we are sure about the plumbing, right :D) though. I'd say the 4148 for diode logic as I have experimented with them in the past (an attempted 4-bit adder failed) 100K resistors should do fine. As said above get your facts before carrying on.
 

flyingnunrt

Senior Member
Thanks all,
The block diagram for the receiver did not look like open collector, but i'm not too familliar with what that should look like either.
yes Hippy, it would appear that 260us might be the limit so I don't need to worry about the 18M just yet, at present using a 08M at 8mHz
I have the system working OK on one sensor at 500us at present
the TX's & RX's will be in tubes and arranged in a couple of totem poles for a beam break set up at 3 or 4 height levels.
The TX's will be driven by one 08M and the RX's detected by another independant 08M
The output will then be sent to a further 18X
 
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