Search found 134 matches

by Chris Foley
Wed May 28, 2003 10:05 pm
Forum: General Discussion
Topic: amp meter shunts
Replies: 9
Views: 2131

Re: amp meter shunts

True, thanks for the help. The first part of the last paragraph in that post should go like this:<p>Rm is your meter resistance. The easiest way to work the shunt problem is to look at it as a current divider. Let's say you want to measure 0 - 1A with this meter. You want 99.999% of the current to g...
by Chris Foley
Wed May 28, 2003 9:32 am
Forum: General Discussion
Topic: amp meter shunts
Replies: 9
Views: 2131

Re: amp meter shunts

Here's another way to do what Dave said:<p>To find the shunt value, you have to know the resistance of the meter, which is probably a taut-band type. You have to be careful measuring the coil resistance of the meter, though, because most ohmmeters will put too much current through the coil, causing ...
by Chris Foley
Tue May 27, 2003 6:14 am
Forum: General Discussion
Topic: Hold reading on LCD meter readout
Replies: 7
Views: 1943

Re: Hold reading on LCD meter readout

On the hobbyist level, and if you'd like to try something different, you might want to take a look at doing a home-brew footcandle meter with a Cadmium Sulfide photocell and an ohmmeter. If you have a DMM with a measurement hold function, you'll be able to get the measurement you need.<p>The CdS pho...
by Chris Foley
Sun May 25, 2003 2:52 pm
Forum: General Discussion
Topic: Battery charger
Replies: 21
Views: 4638

Re: Battery charger

Ooops -- Rodney's right -- my bad. Definitely check the battery type first.
by Chris Foley
Sat May 24, 2003 9:29 pm
Forum: General Discussion
Topic: Battery charger
Replies: 21
Views: 4638

Re: Battery charger

Electronic Circuit Schematics -- Batteries <p>is a good intro to the business of recharging NiCad batteries. You probably have a 10-cell pack, which has a nominal voltage of 12.5VDC (1.25V per cell). First, you want to use a resistor or current sink to discharge the pack to 10V. Then, you charge it...
by Chris Foley
Sat May 24, 2003 3:48 pm
Forum: General Discussion
Topic: AC to DC using a full bridge rectifier
Replies: 3
Views: 1273

Re: AC to DC using a full bridge rectifier

Try looking at this:<p>Electronic Circuit Schematics -- Unregulated DC Power Supply<p>Replace the transformer shown in the diagram with an AC wall wart, and you have an unregulated DC power supply.<p>[ May 24, 2003: Message edited by: Chris Foley ]</p>
by Chris Foley
Thu May 22, 2003 8:20 pm
Forum: General Discussion
Topic: two quickie questions;
Replies: 6
Views: 2026

Re: two quickie questions;

417#'s,442#'s,443#'s? HTL? Or is that RTL? Keep 'em as souvenirs from the '60s, along with your Humphrey bumper stickers. Eventually they might be worth something. 30-12au7's, 18-12ax7's, 2-6L6's, & a 5U4GB. These are fairly common tubes -- you probably aren't sitting on a gold mine with them. Think...
by Chris Foley
Tue May 20, 2003 12:49 am
Forum: General Discussion
Topic: TTL interface
Replies: 10
Views: 2460

Re: TTL interface

db is on the right track. Try getting in touch with the manufacturer of the dental camera. The company that manufactures the camera might have applications people who could give you a hand. By the way, you have read the manual, right? Go through it one sentence at a time, and see if there's any info...
by Chris Foley
Wed May 14, 2003 11:13 am
Forum: General Discussion
Topic: Strain Gauges
Replies: 6
Views: 2107

Re: Strain Gauges

Here it is...<p>Multiplex Signal Conditioner<p>[ May 14, 2003: Message edited by: Chris Foley ]</p>
by Chris Foley
Wed May 14, 2003 11:05 am
Forum: General Discussion
Topic: LM317 and op-amp Constant Current Source
Replies: 20
Views: 4939

Re: LM317 and op-amp Constant Current Source

Almost. You want to use a 10 ohm resistor (10 ohms * 100 mA = 1.0 VDC). That will make it so both inputs of the LM358 are out of the grass (a 1.0 mV input signal is below what the LM358 can handle, and also is dwarfed by the offset). Apart from that, I think you're there. How about just putting some...
by Chris Foley
Tue May 13, 2003 4:20 pm
Forum: General Discussion
Topic: LM317 and op-amp Constant Current Source
Replies: 20
Views: 4939

Re: LM317 and op-amp Constant Current Source

I've created a little confusion here by not being very specific in referring to the circuit. The "high compliance current sink" is shown in the National LM358 appnote, page 15, upper left hand corner.<p> http://cache.national.com/ds/LM/LM158.pdf <p>The LM385 is covered in this data sheet:<p> http://...
by Chris Foley
Tue May 13, 2003 3:15 am
Forum: General Discussion
Topic: LM317 and op-amp Constant Current Source
Replies: 20
Views: 4939

Re: LM317 and op-amp Constant Current Source

The LM385BZ-1.2 is a 1.2V bandgap reference IC in a TO-92 package. It's common, fairly inexpensive, easy to use, and behaves well if you treat it right.<p>National Semiconductor LM185.pdf<p>[ May 13, 2003: Message edited by: Chris Foley ]</p>
by Chris Foley
Tue May 13, 2003 1:46 am
Forum: General Discussion
Topic: LM317 and op-amp Constant Current Source
Replies: 20
Views: 4939

Re: LM317 and op-amp Constant Current Source

Do you mean 100mA +/- 0.05mA? This might be doable with an LM358. (By the way, you might use the other end of the dual to drive an LED which indicates voltage getting too high for constant current).<p>Try working through the appnote example in AN31, using an LM358 and a single supply. Use a well-reg...
by Chris Foley
Sat May 10, 2003 12:33 pm
Forum: General Discussion
Topic: LM317 and op-amp Constant Current Source
Replies: 20
Views: 4939

Re: LM317 and op-amp Constant Current Source

No need to struggle -- just decide ahead of time what kind of precision and drift characteristics you need ahead of time. I'm assuming you need something like 0.1% accuracy, with low drift. For almost all standard current source/sink circuits of that type, you're relying on the feedback provided fro...
by Chris Foley
Thu May 08, 2003 3:59 am
Forum: General Discussion
Topic: LM317 and op-amp Constant Current Source
Replies: 20
Views: 4939

Re: LM317 and op-amp Constant Current Source

Use a low temperature coefficient power resistor with a power rating much higher than the job requirement for the current limiting/sensing. A typical power resistor has much more temperature drift than the LM317, especially if you run it hot. A second important mod is to use a big heat sink to limit...