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5056  Forum 2005-2010 (read only) / Frequently-Asked Questions / Re: Why does my resistor have no effect? on: March 03, 2010, 02:50:28 pm
If you need more than 1 amp, and all you have are 78XXs laying around (and are cheap and lazy like me!), you can parallel the lines together for higher amperages (I would only 2-3 like this, honestly - it would get absurd after that).

5057  Forum 2005-2010 (read only) / Frequently-Asked Questions / Re: Why does my resistor have no effect? on: March 02, 2010, 10:45:23 pm
If you want to get the full 1 amp rating for the 7805, you -must- mount it to a heat-sink (unless you like having smoke/fire-emitting devices around!)...
5058  Forum 2005-2010 (read only) / Frequently-Asked Questions / Re: Multimeter on: March 02, 2010, 04:31:04 pm
Personally, I've never had a problem with the el-cheapo meters from Harbor Freight (discount chinese tool vendor); they tend to last for a fairly long time, they handle light abuse, and the batteries are typically standard 9V.

Not sure how you would be able to tell if there were an issue with one, unless you already owned a quality meter (Fluke or such), then you could probably compare readings...


/not a professional
5059  Forum 2005-2010 (read only) / Frequently-Asked Questions / Re: Is this right board for connecting sensors to a PC on: March 02, 2010, 04:36:33 pm
Also - keep in mind that depending on the tank, usage, and local/State laws (whatever that means in the context of your geographical location), modifying or even attaching such a device (without being licensed, etc) may violate laws; check into this before attempting any such modification, and if in doubt, ask a professional.
5060  Forum 2005-2010 (read only) / Frequently-Asked Questions / Re: Batteries on: January 31, 2010, 05:08:29 pm
If you are planning on running on the on-board regulator (say via the external voltage jack), then you are going to need at least 6 volts (you can go all the way up to 12 volts, IIRC); or 5 1.2 volt NiMH cells wired in series (here is where going with a standard R/C car 7.2 volt NiMH pack makes sense; tons of current available, and easily within the spec for the on-board regulator).

 If you are going to bypass the regulator (as noted by koyaanisqatsi) by connecting to the 5V input pin on the Arduino board, then a 3 or 4 cell pack (3.6 or 4.8 volts, respectively) would work fine; just note that without a regulator, once the battery voltage drops below 3.6 volts, "strange things" will occur (everything from wrong readings on analog pins, spontaneous resets, to just turning off). Also if there are other loads connected to the battery, their power needs may cause the voltage to fluctuate to the Arduino, which could cause similar strange issues; the purpose of the regulator is to deliver the exact voltage needs, regardless of the level of the input voltage (within certain parameters, of course).
5061  Forum 2005-2010 (read only) / Frequently-Asked Questions / Re: Batteries on: January 30, 2010, 10:02:53 pm
I would get name brand myself; you might also see if there is a Batteries Plus near you, they might be able to make you some custom packs (may not be cheap, though). Stay away from Harbor Freight (or any other discount tool seller) rechargeables; I haven't had too much luck with them lasting.

I once actually had pretty good luck with some rechargeable alkalines (yes, they do exist) made by Eveready, IIRC. I don't know if they still sell them or not, but they are available.

Something else: At one time, it was possible to get SLA (sealed lead acid) in C and D cell form (a long time ago, All Electronics carried them surplus). I don't know if they are still made or sold, but that is another option.

Lastly, realize that NiCd and NiMh (and maybe LiIon and LiPoly, but don't quote me on it) only have 1.2 volts per cell, not 1.5; so four cells will give you 4.8 volts, not 6 volts - that may not run the Arduino on the external power connector (I think the onboard 5V regulator needs at least 6-8 volts to work?). A better bet would be to use 7.2V (6 cell) or 9.6V (8 cell) R/C car batteries; some can be "quick charged", and there are really good ones out there that can take a beating - check out your local R/C car hobby shop, let them know what you need/what you are doing, and they can easily hook you up (pick up some servos while you're there!)...
5062  Forum 2005-2010 (read only) / Frequently-Asked Questions / Re: 3 axis stepper sheild for arduino on: February 26, 2010, 04:21:31 pm
Making it a separate board with an on-board Arduino processor would probably be the best idea.

There is already a user here on the forums who has made an Arduino-based CNC system, and put a small g-code interpreter on it (if you still had room to include such code, that would be a pretty amazing product!).

Also - if you could add the ability to switch on/off one or two other high-current loads, that would be perfect (so you can switch the spindle motor, blower or vaccuum motor, or coolant pump on and off).

Sounds like an awesome project!
5063  Forum 2005-2010 (read only) / Frequently-Asked Questions / Re: panning a PING: code check! on: February 25, 2010, 12:06:00 am
Something I had thought about my reply: what happens if the ping isn't received back? You essentially get stuck. What you would probably want to do is somehow implement a timer that is started when the ping is sent out, then checked periodically and if the time elapsed is greater than say what the time it would take to cover 30 feet or so (or whatever your max sense distance is), count it as "no object" and move on.

Sorry about the oversight...

5064  Forum 2005-2010 (read only) / Frequently-Asked Questions / Re: panning a PING: code check! on: February 23, 2010, 04:47:40 pm
You kinda have to do those steps, because it takes a certain amount of time for the sensor to fire and receive a return (speed of sound); you can't move the sensor before it gets the return echo back.

Maybe you could approach this another way:

1. Fire the ping; on the return echo activate an interrupt.

2. In the interrupt, store the value, rotate the servo a little.

3. If at the "end of travel" (whatever that means to you), reverse the direction of the servo or position it back "home" (whereever that is).

4. Go back to step 1

This way you would only be moving the servo on receipt of the echo, running the system as fast as the ping sensor will go, not as fast as the servo will go.

It will still be choppy, but hopefully less so.

You might also mount the ping on a stepper, instead of a servo (but you will need some other kind of position feedback); you might be able to get better angular resolution this way.

If none of that works to your satisfaction, then you may want to look into a custom "flying spot" LIDAR ( system (not cheap, not easy, but definitely homebrew-able!).
5065  Forum 2005-2010 (read only) / Frequently-Asked Questions / Re: Need help with discontinued transistor on: February 25, 2010, 05:50:11 pm
Actually, it could be acting as a heat sensor!

I seem to recall that some transistors when hooked up in a weird manner (or even a sane manner) will change values, etc based on temperature. Theres even a way to use a transistor in such a manner to get "noise" out of it for a true random number generator (very useful for encryption).

So maybe it is? You can't really know unless you have the schematic handy (and even then it may be difficult to tell)...

5066  Forum 2005-2010 (read only) / Frequently-Asked Questions / Re: Need help with discontinued transistor on: February 25, 2010, 05:06:05 pm
Alright - now you're cross posting, and that looks bad (nettiquette and all); you're off the hook this time...


As far as what the weird config is for, with a picture of what is going on, who knows? How are the leads connected? Is it arranged in some weird form of darlington? Maybe they were stacked to conserve space or use the same heatsink (doesn't sound like a great design, though)? Maybe they were stacked (and if the leads are in parallel) added together for slightly more current handling?

Any number of possibilities, and analog design like that is not my forte, unfortunately. You might have better luck regarding this if you post on a board for vintage (is it vintage) audio amplifiers or stereo/hifi enthusiasts...

Good luck getting it fixed!

5067  Forum 2005-2010 (read only) / Frequently-Asked Questions / Re: Need help with discontinued transistor on: February 25, 2010, 11:22:01 am
I have never seen an electronic part that looks like a transistor without being one.

First off, I am glad you found it (having the right part number helps, doesn't it?).

Second; the part I showed you (2N882) came in 3-pin TO-18 and TO-92 cases - it isn't a transistor, but I can guarantee you that transistors do come in those case styles (the 2N2222 NPN generally is seen in a TO-92 case; older transistors are often seen in TO-18 cases), which is why I mentioned the part.

Just because it looks like a transistor doesn't mean it is one.

I have some parts that I believe are "house numbered" that look like TO-3 packaged transistors (I was hoping for a 2N3055 equivalent), but they don't ohm out like any transistor - they may be a form of MOSFET, but I have yet to find out how to ohm out a MOSFET. I am on the verge of building a transistor tester just to be able to figure them out...

5068  Forum 2005-2010 (read only) / Frequently-Asked Questions / Re: Need help with discontinued transistor on: February 24, 2010, 11:35:06 pm
It couldn't be a 2N882, could it?:

That's not a transistor, though (are you sure its a transistor?)...
5069  Forum 2005-2010 (read only) / Frequently-Asked Questions / Re: Home Automation on: February 15, 2010, 03:44:45 pm
In theory, yes (you're going to need a bunch of glue code, though).

Not to deter you from using an Arduino, but using one technically complicates matters; there are tons of USB interface boards out there to allow digital i/o control, relay control, analog i/o, etc - all via simple USB interfaces (in many cases done with FTDI USB serial, like the Arduino).

Now - if your goal is to replicate one of those boards, and to use the Arduino in the development (ie, creating an embedded controller with a command set to control various relays and such - based on an ATMega uC); that is one thing. But if your end goal is just control of lights and such, other solutions are readily available, and save you that much extra effort (believe me, writing the controlling code and interfacing to all of the external lights and such will be tough enough).

Just a thought...good luck.

5070  Forum 2005-2010 (read only) / Frequently-Asked Questions / Re: not LEDs on: February 20, 2010, 04:18:28 am
Ok, so we know it works; we also know that in some manner we can scale it up to full sized bulbs, but the question is "what to control them with"?

SCR? Triac? SSR?

I want to say "for a beginner" that the SSR is the way to go; but if you had the experience (to wire everything up and make it safe), then one of the first two would probably be best (smaller package and such, but you would still need heat-sinking, likely)...


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