Help understanding schematic

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I am going to make some optocoupler interfaced inputs on my AVR
and i am trying to use (borrow the ideas from) this schematic.

Its an Olimex board , that has 4 optocoupler inputs.

What i dont understand is the 1N4148 across the input , why is it there ??
is it just a protection if you reverse the VCC so that it is on the lower side or ????

http://www.olimex.com/dev/images...

Thank you for any hints/help

/Bingo

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looks like they are just for what you were thinking. reverse voltage protection. i would think that from what i see.

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LEDs have a fairly low reverse breakdown voltage. The 1N4148s protect them.

j.

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So if im 100% sure i connect the things correct i dont need it ???

/Bingo

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rAs long as you don't use AC voltages and only use the right polarity then you don't need them.
I you connect it, then you can use the inputs for AC voltages.

You don't need to connect the LED's either, if you don't need to see if the input is high or not.
Just remeber to increase the resistor if you remove the LED.
The resitor value should be chosen depeding of the input voltage you want to interface.
IT's the current through the optocouplers that are important

Here is a new great alternative to using optocouplers:
www.isoloop.com
Analog Devices makes similar and pin compatible devices to the isoloop devices.
These devices are superiour to optocoupler in speed and current consumption.
You can also get more compact soloutions with many isolated in/outputs in the same device.

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AndersAnd wrote:

...Here is a new great alternative to using optocouplers:
www.isoloop.com
Analog Devices makes similar and pin compatible devices to the isoloop devices.
These devices are superiour to optocoupler in speed and current consumption.
You can also get more compact soloutions with many isolated in/outputs in the same device.

How do they compare in price to a more-or-less equivalent opto?

Lee

You can put lipstick on a pig, but it is still a pig.

I've never met a pig I didn't like, as long as you have some salt and pepper.

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theusch wrote:
How do they compare in price to a more-or-less equivalent opto?

They are cheaper, but you can't really get optocouplers as fast as these devices.

I have only compared digital input optocouplers with digital input IsoLoop.
I was going to use two 3.3V Agilent HCPL-063L for a project, to get 4 isolated 5 -> 3.3V logic inputs. A speed of 10Mbps is requird for the project.
Instead I can use one ADum1400 or IL715-3 which also comes in much faster versions than optos.

All prices are from Digikey:

Soloution with 4 channels in same directon:

NVE IsoLoop:
1 * IL715-3 (110Mbps): $7.46 (16 pin 0.15'' SOIC. Narrow)
1 * IL715 (110Mbps): $7.46 (16 pin 0.30'' SOIC. Wider housing for better high voltge isolation)

Analog Devices iCoupler:
1 * ADuM1400ARW (1Mbps): $5.20
1 * ADuM1400BRW (10Mbps): $7.88
1 * ADuM1400CRW (90Mbps): $8.37

Agilent High Speed LVTTL Compatible 3.3 Volt Optocouplers:
2 * HCPL-063L (15Mbps): 2 * $4.50 = $9.00 (Two 8-pin ICs needed to get 4 inputs)
4 * HCPL-060L single optos could be used for a total of $8.00, instead two dual optos, but this requires four 8-pin ICs instead of two.
(Four additional currrent limiting resitors are needed for the opto LEDs in these soloutions).

If you need an odd number in and outputs, the IsoLoop / iCoupler soloution becomes even cheaper compared to optos.

If you need 1 input and three outputs you need the opto ICs (one dual and two single); with IsoLoop / iCoupler you can still use only one IC. They even have packages with 5 in/outputs and some special suited for RS485 isolation.

Soloution with 1 channel in one direction and 3 chaneels in the other direction:

NVE IsoLoop:
1 * IL717-3 (110Mbps): $7.46 (16 pin 0.15'' SOIC. Narrow.)
1 * IL717 (110Mbps): $7.46 (16 pin 0.30'' SOIC. Wider housing for better high voltge isolation)

Analog Devices iCoupler:
1 * ADuM1401ARW (1Mbps): $5.20
1 * ADuM1401BRW (10Mbps): $7.88
1 * ADuM1401CRW (90Mbps): $8.37

Agilent High Speed LVTTL Compatible 3.3 Volt Optocouplers:
1 * HCPL-063L + 2 * HCPL-060L (15Mbps): $4.50 + 2 * $2.00 = $8.50 (Three 8-pin ICs)
Alternative opto soloution: 4 * HCPL-060L (15Mbps): 4 * $2.00 = $8.00 (Three 8-pin ICs)
Four additional currrent limiting resitors are needed for the opto LEDs in these soloutions.

So instead of using 4 * HCPL-060L (15Mbps) 8-pin devices for $8.00, you can get 1 * IL717-3 16-pin(110Mbps): $7.46.
I would prefer one 16-pin IC that is cheaper, faster, consumes less power instead of 3-4 8-pin ICs that also need current limiting resistors for the LEDs.

These ICs are ideal to for example isolate a SPI bus conneted to an ADC for example.
Or you can make an isolated ISP programmer with only one IC.
You can also get special ICs made to isolate the USB bus or RS485 bus.

You can order samples from both NVE and Analog Devices:
NVE: http://www.isoloop.com or www.nve.com
Analog Devices: www.analog.com

Last Edited: Wed. Oct 13, 2004 - 10:37 PM
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From a fast look around there aren't comparable devices. They seem to be a lot faster and a fair bit more expensive.

Ralph Hilton

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rhilton wrote:
From a fast look around there aren't comparable devices. They seem to be a lot faster and a fair bit more expensive.

They are cheaper than comparable optos allthough you can't get 110Mbps optos.
But maybe you can get some low-end slow opto soloution that is cheaper than these devices.

One of the best thing about these 4 channel devices are that you can get some with 1 in + 3 out (or reverse), 2 in + 2 out, 4 in/out.
You can also get five channels and 1+1 one channel or 2 channel, RS485 devices, USB devices, and 1 channel devices.

Maybe the analog optos are cheaper than the analog IsoLoop's. I have only compare the digital devices.

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Here's NVE's own 10 reasons to use the IsoLoop devices instead of optocouplers:

10 Reasons to Kick the Opto Habit
http://www.nve.com/products/isol...

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Bingo600 wrote:
So if im 100% sure i connect the things correct i dont need it ?

It depends on what you connect it to. If its sensing any inductive loads being switched, like relay coils that generate large reverse voltages, then the diode will be needed.

If its for a product where you will not always be in control of what gets hooked to it, then you need the diode.

If its in such a "tame" controlled design where nothing will ever get hooked up wrong then maybe you do not need the entire isolator at all and something else will work better?

BTW, thanks for the great isolator product info AndersAnd.

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Mike B wrote:
BTW, thanks for the great isolator product info AndersAnd.

You're welcome.
I haven't tried them yet, but I will probaly use them for a 10Mbps projcet as I mentioned.
From the data sheets they look very interesting compared to optos. I can't find any drawbacks for my purpose, only improvements.

Until recently I had not heard of them, but ran across an article about the IsoLoop.
Later I found out that Analog Devices have started to make similar devices in (almost) pin compatible housings.
After I found them, I hvave been reading more articlesabout them and everyone only had positive things to say about them.
Except one little detail, I think it was something about you don't know what state they are in when you power them up. In somet special cases it's nessasary to cycle the input after power up, to be sure of the output state.

There's a good article about them in Circuit Cellar issue 142 May 2002.
The article is called: You're Not Alone Dealing with Isolation.
You can download the article here: http://www.circuitcellar.com/lib...

I also saw the IL717 used in a digitally controlled Quad Bench Power Supply supply to isolate the SPI port of an AT90S8535 AVR from ADCs and digital pot's.
This project is published in Circuit Cellar issue 149 December 2002
The project is called: Quad Bench Power Supply
Download the article: http://www.circuitcellar.com/lib...
Bascom BASIC source code and firmware: ftp://ftp.circuitcellar.com/pub/...

This would be a nice DIY project to use both AVR and IsoLoop ICs.

Maybe I should make this project some day, allthough the source code is in BASIC :(
My BASIC skills are not so good, but maybe I should try to convert the source code to C and change the AT90S8535 to an ATmega8535 at the same time.

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Thanx for the ansgers guyzz :D :D

Btw: Its going to be input from some Mega32 pins , but its on a board allready containing optos 4N37 i think.

/Bingo