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Open Collector Circuits

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Gandledorf

New Member
Could someone who is more familiar with schematics please help me with something? In the circuit description of the IR detectors I am looking at (https://www.vishay.com/doc?80069) it shows a resistor between V+ and Vout, am I correct in assuming this is a pullup resistor, and thus the device is open collector? If so this means a device can only pull the line down, not up, and thus I can hook them up in series, correct?

Thanks again, you guys have been so much help!
 

Gandledorf

New Member
crust said:
Yes, it is a pull-up and can only pull the line to ground. I dont know what you mean by connect them in series though.

What I mean is this: Each IC has Vin, GND, and Vout. Can I take two such recievers, place them back to back (to give near 360 degree coverage), and connect both Vout's to the same pin on a uC as they can only pull it down?

(We are assuming that if they both see a source, it will be the same source. For my purposes, this is a fairly valid assumption)
 

laroche73

New Member
OC circuits

I can hook them up in series, correct?
Yes, I think you meant to say "in parallel", it's also called a "wired-or" configuration. No specs on the pullup, but I believe these modules use a pretty high value (50 - 100K?).
 

Gandledorf

New Member
Re: OC circuits

laroche73 said:
I can hook them up in series, correct?
Yes, I think you meant to say "in parallel", it's also called a "wired-or" configuration. No specs on the pullup, but I believe these modules use a pretty high value (50 - 100K?).

30k according to the data sheet, why does it matter?
 

Gandledorf

New Member
laroche73 said:
30k according to the data sheet, why does it matter
you can use a lower valued external pullup resistor if you need faster switching times.

Is there a way to determine the switching times? I'm limited by the speed of my IR diode mainly, and as the same company makes both the diode and reciever, I'd bet they are well matched.
 

laroche73

New Member
OC output

A lower valued external pullup can help speed up the risetime of an open-collector output stage, at the expense of drawing additional current during switching. In this case, other parts of the IR module limit your data rate, but they're present for good reasons, (noise immunity). In particular, the integrator limits the minimum burst length and the minimum time between bursts. Adding an external pullup (>= 4.7K) may help if you're trying to run a module near it's rated maximum speed.
You've probably noticed Vishay makes other IR modules rated for higher speed data rates, the TSOPx1xx series handles short bursts up to 4kbps, and the TSOP7000 data rates up to 20k. Notice the value of the pullup resistor in the internal output stage is reduced accordingly (TSOP12 -30K, TSOP11 - 25K, TSOP7000 - 10K). It's a tradeoff though, higher data rates mean less noise immunity and shorter transmission distances.
 

Gandledorf

New Member
Re: OC output

laroche73 said:
A lower valued external pullup can help speed up the risetime of an open-collector output stage, at the expense of drawing additional current during switching. In this case, other parts of the IR module limit your data rate, but they're present for good reasons, (noise immunity). In particular, the integrator limits the minimum burst length and the minimum time between bursts. Adding an external pullup (>= 4.7K) may help if you're trying to run a module near it's rated maximum speed.
You've probably noticed Vishay makes other IR modules rated for higher speed data rates, the TSOPx1xx series handles short bursts up to 4kbps, and the TSOP7000 data rates up to 20k. Notice the value of the pullup resistor in the internal output stage is reduced accordingly (TSOP12 -30K, TSOP11 - 25K, TSOP7000 - 10K). It's a tradeoff though, higher data rates mean less noise immunity and shorter transmission distances.

Well, as I am passing very little data (only a packet of 10 bits (8 data + start + parity)), and I would like to achieve transmission distances on the order of 100-600m, I suppose the lower transmission rates will be the best.

Hopefully I can get these distances. I'm using the TSAL6100 IR emitter (1A pulsed at 10kHz yields 1000 mW/sr), and collimating the beam to help achieve these ranges.
 

Gandledorf

New Member
The Real MicroMan said:
this has an INTERNAL pull-up. Read the very last section in the data sheet

If you had read the first message in this thread, you would have seen we already acknowledged that, and were just discussion the merits of using an external pull-up of a lesser value to increase the switching speed.
 

Nigel Goodwin

Super Moderator
Most Helpful Member
Re: OC output

Gandledorf said:
laroche73 said:
Well, as I am passing very little data (only a packet of 10 bits (8 data + start + parity)), and I would like to achieve transmission distances on the order of 100-600m, I suppose the lower transmission rates will be the best.

That's some distance! - from 10-60 times the range that you get without any optics. I'll be very interested to hear how you get on!.
 

crust

Member
I recall several years ago a system that used lens to focus a high power led about 2km. As I recall the tricky part was getting the transmitter and receiver properly lined up. They used a mechanical solution which incorporated a gun scope (or something that looked like it) for calibration.
 
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