## Search found 134 matches

Tue May 06, 2003 8:11 pm
Forum: General Discussion
Topic: voltage limiting relay
Replies: 12
Views: 2435

### Re: voltage limiting relay

Try this:<p> Simple PWM Circuit <p>Replace R10 with a 2.2K resistor to drive a PNP (2N3906)with its emitter tied to V+. You then use the collector output to drive an NPN darlington transistor, such as the ON Semi MJ11028. Connect a 100 ohm 2W resistor between the collector of the PNP and the base of...
Mon May 05, 2003 6:03 pm
Forum: General Discussion
Topic: voltage limiting relay
Replies: 12
Views: 2435

### Re: voltage limiting relay

Why didn't you say so? One of the things you might want to try is Pulse Width Modulation (PWM) control. Actually, they're talking about that in another post right now<p> Diode or No Diode? <p>By turning on and off a MOSFET or power transistor at a relatively high rate (say, over 2KHz or so), you can...
Mon May 05, 2003 2:47 pm
Forum: General Discussion
Topic: voltage limiting relay
Replies: 12
Views: 2435

### Re: voltage limiting relay

Ohm's Law:<p>V = I * R<p>where V is voltage in volts, I is current in amps, and R is resistance in ohms. Use this equation and you can figure out what you need. What you're looking at is called a "dropping" resistor, which shares the power with the load. This only works, by the way, if you have a lo...
Sun May 04, 2003 8:22 pm
Forum: General Discussion
Topic: voltage limiting relay
Replies: 12
Views: 2435

### Re: voltage limiting relay

Do you mean a type of relay that is open circuit when off, and then when turned on, changes the 12VDC to 6 to 9 VDC? If so, the simplest thing would be to use a relay rated for 40 amps, and use an 0.1 ohm, 200 watt power resistor in series with the load. These resistors are commercially available su...
Sat May 03, 2003 5:34 am
Forum: General Discussion
Topic: in need of a capatior
Replies: 10
Views: 2511

### Re: in need of a capatior

Possibly this has to do with the intercom circuit in a previous post? You might want to try scrounging one from an old phone with an electromechanical ringer -- I think they all had them.
Fri May 02, 2003 6:21 am
Forum: General Discussion
Replies: 8
Views: 2001

Some practical suggestions: First, check the voltage rating of the cap. You should have a cap rated at least 150V, and it should be a non-polarized cap (it sees AC). Also, try putting a 10K 2W resistor as a load instead of the cap, and see what happens. This waveform is not a sine wave, and it's not...
Sun Apr 27, 2003 5:29 pm
Forum: General Discussion
Topic: Ph meter.
Replies: 8
Views: 2254

### Re: Ph meter.

There was a small topic a couple of months back on a similar issue:<p> pH meter <p>The first place you should look is Omega Engineering:<p> Omega Engineering <p>They have a number of pH meters available for very reasonable cost, with RS232 output. Their website also has a lot of technical informatio...
Fri Apr 25, 2003 8:25 pm
Forum: General Discussion
Topic: Senior project idea
Replies: 11
Views: 2560

### Re: Senior project idea

Hi, Chess. It looks like "In for a penny, in for a pound". Since you've already done making dot-matrix displays from individual LEDs, it shouldn't be too much more trouble to do the drivers out of individual transistors. Check the multiplex ratio. If you do 32:1, any permissible amount of LED curren...
Sun Apr 20, 2003 2:53 pm
Forum: General Discussion
Topic: Video Camera Detector Schematic?
Replies: 27
Views: 5728

### Re: Video Camera Detector Schematic?

BTW, gadgeteer, what is the link to that Electronics Circuit Schematics page? Thanks, and sorry for getting off the subject!
Wed Apr 16, 2003 8:05 pm
Forum: General Discussion
Topic: Multiplex Signal Conditioner
Replies: 7
Views: 2112

### Re: Multiplex Signal Conditioner

Hi, Ian. Will's right. Strain gauges can be a bear to interface. You have a number of separate problems. Strain/resistance is kind of non-linear. You need a tempco compensation for the metal you're placing it on You have to worry about self-heating changing the reading. Microvolts count big time, ev...
Sun Apr 13, 2003 8:07 pm
Forum: General Discussion
Replies: 16
Views: 4666

### Re: Shortwiring AC/DC power adapter

Throw out suspicious wall warts, just on principle. Seriously, wall warts are generally made "just good enough". If the beast has been stressed, it may have heated the wiring on the transformer, possibly causing a partial short in the primary or secondary wiring, or melted wire insulation, causing a...
Sun Apr 13, 2003 12:52 am
Forum: General Discussion
Topic: de bounce
Replies: 6
Views: 3816

### Re: de bounce

Hi, mj. I would take a look at your physical setup first, like some of the prior postings said. Most float switches have some hysteresis built in, but if you have agitation on the surface of the liquid, that can cause problems. Also, many float switches aren't meant to drive an inductive load like a...
Fri Apr 11, 2003 3:27 am
Forum: General Discussion
Topic: pic ICE
Replies: 2
Views: 843

### Re: pic ICE

Thu Apr 10, 2003 5:30 am
Forum: General Discussion
Topic: water sampler
Replies: 10
Views: 2427

### Re: water sampler

Yes, multiple permutations, lowest installed cost, meeting project specs. I was thinking, with a 36:1 ratio, it might be better to use gearing instead of multiple belts/pulleys. Most projects are that way. The longer you look at them, the more ideas and permutations come to mind. Eventually you have...
Wed Apr 09, 2003 8:28 pm
Forum: General Discussion
Topic: water sampler
Replies: 10
Views: 2427

### Re: water sampler

Hmmn. Filtering floating fish feces. Fascinating. (Sorry -- I couldn't pass it up!)<p>I'm assuming you would require a certain amount of accuracy in the pump volume(say, +/- 1 or 2%) If you have a budget, I'd recommend a small peristaltic pump. They're available from Cole-Parmer (general-purpose lab...