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[DPRG] Board indication of 120VAC

Subject: [DPRG] Board indication of 120VAC
From: Kipton Moravec kmoravec at spectronics.us
Date: Wed Jun 1 15:44:35 CDT 2005

Here is the deal.  This is going into a production unit. About 300 per month
is what they are telling me. There are 7 120V indicators on the board. The
indicators are used only for visual conformation that the circuit has turned
on a pump (and the fuse is not blown). The PLC does not need conformation.

My first pass looking at it was with a Neon light, and I was surprised they
ran at 90V. But they would have to be hand placed on the board and they
about the same price as an 0805 LED, a S1G diode, and a 250V 0.1 surface
mount capacitor.  I would rather have surface mount than something that
needs hand placement even though there will be hand placed connectors the
rest of the board is surface mount., In addition the LED will look like
other LED's on the board.

I have done the other trick Rick mentioned with a LED and 30K resistor. (DC
Circuit) Ohm's Law: V = IR
120 = I * 30000 or I = .004 or 4 mA. That is 0.48W dissipated in the
resistor.  The resistor gets very warm.  I did not want to do that with 7 on
the board in a closed box.

Kip
  -----Original Message-----
  From: dprglist-bounces at dprg.org [mailto:dprglist-bounces at dprg.org]On
Behalf Of jdrumm9015 at aol.co 0
   m
  Sent: Wednesday, June 01, 2005 1:15 PM
  To: rbickle at swbell.net; kip at kdream.com; dprglist at dprg.org
  Subject: Re: [DPRG] Board indication of 120VAC


  Kip,
    I couldn't resist adding one more option for your on board indicator of
120VAC.
  What about old technology, a neon light bulb?  An NE-2 (?) triggers at
90VAC, a rather
  modest resistor in series is all that is additionally required.  However
if you need to connect
  this to a microcontroller circuit like Rick pointed out, the neon light
won't work.

  John Drummond

  -----Original Message-----
  From: Rick Bickle <rbickle at swbell.net>
  To: kip at kdream.com; 'dprglist' <dprglist at dprg.org>
  Sent: Mon, 30 May 2005 11:39:06 -0500
  Subject: RE: [DPRG] Board indication of 120VAC


Kip,

If your 110vac detection circuit is going to connect to a
microcontroller circuit, you should isolate the 110 from the rest of the
circuit. Try using a H11AA1 bidirectional optocoupler with a 47K 1/2
watt dropping resistor on the LEDs. If you're looking for a voltage
threshold, use a 1.5KE90CA or similar bidirectional diode in series with
the HV end and drop the resistor value accordingly.

If you just need an indicator, an LED with 1N4004 diode and 27K or so
dropping resistor will do the trick.

Rick


-----Original Message-----
From: dprglist-bounces at dprg.org [mailto:dprglist-bounces at dprg.org] On
Behalf Of Kipton Moravec
Sent: Saturday, May 28, 2005 2:01 PM
To: dprglist
Subject: [DPRG] Board indication of 120VAC


I am working on a board design and I need a circuit that indicates if a
120VAC contact is on or off.  Ideally this would be a 120V lamp that can
be surface mounted on a PCB. Unfortunately I can't find one.

There are 6 of these needed and since this will be a production board I
need a cheap and easy way to do this.

The cheapest way is with a diode, resistor, and LED in series. But
dropping 120V @ 8-10 mA across a resistor gets very hot very fast. That
is about 1W of energy per circuit * 6 circuits, which means I may need a
fan in the enclosure.  Not what I was wanting.

The other option was a transistor/mosfet and a PWM signal but
controlling it from the isolated side of the step-down transformer was
giving me some concern.

The last option I could think of was based on the Atmel document.
http://www.atmel.com/dyn/resources/prod_documents/doc2508.pdf
But use it to drive a HEX INVERTER driving a LED instead of the Atmel
chip. When I have power the light is on.

Anyone with other ideas?

Kip
--
Kipton Moravec <kip at kdream.com>

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