Skip to main content

Folks,  follow up to the items in the Mtg itad thread.

Well, unless the opto couplers are drawing a lot of current, I think the debounce is complete with the 330uf caps! "

GRJ, Lol good point on the caps.  I should have added 'if required' to "in the software".

"@stan2004 posted:

What is the optoisolator you show in your schematic?

Note that if the purpose of the bridge-rectifier is AC-to-DC conversion at signal levels/currents (as opposed to power levels/currents) you might consider replacing the bridge rectifier with an AC-input optocoupler. "

Stan, the optoisolator place holder in the schematic is a prefab 2 channel board of which I have 4 or 5 on hand.  When designing my board I simply placed two 4-Pin female headers the proper distance apart so the prefab (male pins) drop in for easy replacement.  Looks like the chip on the board is D216.  Yes, my intent is to provide a 5v signal level output to an Arduino Mega 2560 Pro Mini.

"@bmoran4 posted:

I've successfully used the LTV-8x4 series optocouplers with track level AC inputs behind a current limiting resistor: https://optoelectronics.liteon...0series%20201509.pdf"

"@stan2004 posted:

Separately, I think you're dodging a bullet when you tie together the 2 bridge rectifiers as indicated above.  A bridge rectifier does not provide electrical isolation.  It is electrical isolation that "allows" you to tie together the grounds of different electrical circuits.  You dodge the bullet in this case because your input resistor limit the current but if, for example, Track 1 and Track 2 AC power are out-of-phase, then the diode(s) in the bridge rectifier will electrical short the two tracks."

Stan, the layout's track is powered by two 180W bricks, tied to a single ZW-C and properly phased.  But good catch and certainly gives me pause for thought.

bmoran4 and Stan, since reading your posts and investigating the LTV-8x4 chip I'm leaning toward that approach.  Never opposed to building a better mousetrap.  FWIW, I did try to investigate AC optocouplers but all I could ever find were industrial grade (too large and/or too pricey).  These LTV-8x4 chips seem to be spot on for this application.  Any thoughts on the current limiting resistors?

Thanks for all the input so far!

Barry

Original Post

Replies sorted oldest to newest

@barnun posted:


...

Stan, the optoisolator place holder in the schematic is a prefab 2 channel board of which I have 4 or 5 on hand.  When designing my board I simply placed two 4-Pin female headers the proper distance apart so the prefab (male pins) drop in for easy replacement.  Looks like the chip on the board is D216.  Yes, my intent is to provide a 5v signal level output to an Arduino Mega 2560 Pro Mini.

...bricks, tied to a single ZW-C and properly phased.

...  These LTV-8x4 chips seem to be spot on for this application.  Any thoughts on the current limiting resistors?



Regarding the current limiting resistors, I was just going to comment that you choose them the same way you did for your existing optoisolators.  But if I understand it, your existing optoisolators are purchased modules that you did NOT "design" it yourself?

That said, just do a search for optoisolator or optocoupler design.  It's not just the input resistor(s) to play well with the 18V AC track voltage but also the output resistor (and smoothing capacitor if needed) to play well with the 5V Arduino connection.

I could just give you some ballpark values that would probably work with a typical AC optoisolator but better to confirm which exact optoisolator chip you plan to use.  Also, if you want to only use components you already have like the existing resistor and 330uF capacitor then this would be more challenging.

@stan2004 posted:

.... your existing optoisolators are purchased modules that you did NOT "design" it yourself?



Stan, that is correct.

The value of the smoothing cap on the output side is dependent on the load on the opto output, I'm assuming 60hz as the input voltage.

GRJ, 60hz is correct.  On the output side the Arduino should not sink more than 20mA at 5VDC.

Gentlemen, as always thanks for your input.  Filing this away for the moment.  Since I have 5 of the original boards with the bridge rectifier, 330uF cap and the optoisolator design on the way I thought I would wait until they get here, assemble a prototype and do some testing.  Based on those findings I will look at designing a board with either the LTV-824 or the ACPL-214-500E chips and more appropriately sized capacitors and resistors.

Thanks again,

Barry

Something along the lines of 10uf caps will be sufficient I suspect.  My sound board uses a 1uf cap into a 10k load, and it's filtering 60hz from the opto just fine.  The output voltage from the opto when triggered with 60hz hardly moves at all on the 'scope.

GRJ, excellent!  Now I have to dig into the stash to see if I have any 10uF caps.  With my luck I will most likely have some (but at the wrong voltage).

In case any interested party runs across this in the future .... Received the pcb's & parts, got a prototype board together and tested.  The first iteration was using 1K resistors on the AC Line side (R1A & R2A) and failed the finger test (man, were they toasty).  Subsequently tried 1.5K, 2K, 2.7K and wound up using 3k.  The board seems to be working as designed and ran a 24hr. test with no problems.  Attached are the updated schematic and pcb picture, hopefully I can put this one to bed.

BarryIR Detector V2

IRD pcb

Attachments

Images (2)
  • IR Detector V2
  • IRD pcb
@barnun posted:

... The first iteration was using 1K resistors on the AC Line side (R1A & R2A) and failed the finger test (man, were they toasty).  Subsequently tried 1.5K, 2K, 2.7K and wound up using 3k.

Right.  With, say, 18V on the track, the opto diodes only require about 1V.  So the resistor is dropping about 17V.

Power (Watts) = Volts x Volts / Ohms = 17 x 17 / 1000 = 0.3 Watts.  Those look like 1/4W resistors?  But whether 1/4W or 1/2W they're still burning 0.3 Watts which can make even a 1/2 Watt resistor toasty!

At 3K, the resistor is only burning 0.1 Watts which is fine for a 1/4W or 1/2W resistor.

Add Reply

Post
OGR Publishing, Inc., 1310 Eastside Centre Ct, Suite 6, Mountain Home, AR 72653
330-757-3020

www.ogaugerr.com
×
×
×
×
Link copied to your clipboard.
×
×