Philip Martin Wrote:

>  Is there
> >anyway to figure this out with a multimeter?  Let's say it uses 50
> >milliamps.
>
> Yes, measure the resistance of the filament, now apply Ohms Law. Here
> once
> again we assume its a filament lamp were are talking about, cos if its
> an
> LED this don t work, and anyway an LED will only draw something in the
> order
> of 10 to 25 milliamps.
>
> Once you have the resistance of the lamp, divide the voltage the lamp
> will
> be running at by the resistance and you have the current.
>
>
          I hate to nit-pick, but dividing the operating voltage by the
cold filament resistance will give you in rush current, not operating
current. Filament resistance goes up quite a bit once it heats up. If
the specs are unknown on the lamp, then you're better off hooking the
lamp up to a variable power supply and measuring the current drawn at
the desired voltage. Three "fresh" flashlight batteries (AA, C, or D) in
series will get you 4.5 volts, close enough to 5V for a good estimate.
I'd feel much safer driving a incandescent lamp with a cheap switching
transistor such as a 2N2222, than trying to drive it directly from a PIC
I/O pin.

        BTW, anybody got a link for low voltage lamp specs/cross
reference?

        As I side note, I have changed the only applicable setting I can
change on my mailer (Outlook) to send to this address in plain text. The
last time I posted to PICList since I was switched over to NT/Outlook, I
had a few people "scream" at me for posting binary garbage. If some of
you still receive binary garbage attached to my messages (please let me
know - if you get garbage attached), then I'm afraid I'll have to cease
posting all together and simply read PICList.

Frank Richterkessing
GE Appliances
frank.richterkessing@appl.ge.com