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[DPRG] Board indication of 120VAC

Subject: [DPRG] Board indication of 120VAC
From: jdrumm9015 at aol.com jdrumm9015 at aol.com
Date: Wed Jun 1 13:15:24 CDT 2005

  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


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.


-----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.
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?

Kipton Moravec <kip at kdream.com>

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