Show Posts
Pages: 1 ... 15 16 [17] 18 19 ... 22
241  Forum 2005-2010 (read only) / Interfacing / Re: Can an Arduino send a dialup email message? on: January 16, 2009, 11:30:07 pm
It sounds to me as if an arduino and any external modem should be fine. Three points though... 1: If power is problem or not reliable you could power both the arduino and modem off of a battery. In fact, with a transistor or relay you could have the arduino power up the modem when needed, dial out, and shut it back off. Which leads me to point 2: The arduino only needs to send the temperature or at least a message, when the temperature is outside of normal bounds. No need to dial out every 30 minutes if nothing is wrong. And 3: The arduino serial output is TTL. The external modem will want RS232. You would probably need a MAX232 chip.
242  Forum 2005-2010 (read only) / Interfacing / Re: Backfeed on TX/RX lines on: January 27, 2009, 01:09:54 pm
Well, you can't use diodes at the RS232 side as those signals are AC. You might be able to get away with a diodes which have a .3V drop (and put them between the arduino's pins and the adapter.) I'd imagine that the TTL to RS232 adapter would be tolerant of signals coming in at 0 - 4.7V. I'm not so sure if they'd like a .6V drop though.
243  Forum 2005-2010 (read only) / Interfacing / Re: Is it possible to indicate the power of a battery? on: January 27, 2009, 12:00:27 pm
Yes, technically the V slope of LA and LIon batteries is worse but it does make measuring easier. And, in some cases it's not a big deal. If you are powering an arduino through a LM317 or LM7805 then the extra voltage is dissipated as heat anyway so the lower the voltage the less heat needs to be removed.
244  Forum 2005-2010 (read only) / Interfacing / Re: Is it possible to indicate the power of a battery? on: January 26, 2009, 04:53:13 pm
Yes, in fact that is pretty much what laptops do when you run the calibration routine.
245  Forum 2005-2010 (read only) / Interfacing / Re: Is it possible to indicate the power of a battery? on: January 26, 2009, 02:47:10 pm
Yes, it's doable. Batteries tend to change in voltage as they discharge. A fully charged lead acid 12V might actually be about 13.4V. As it discharges it goes down. Usually a 12V battery is considered dead when it hits about 10.5V. So you can test the incoming voltage. Having said that you need to keep a few other things in mind:

1. The discharge curve is not necessarily linear. It might drop off a lot for a while then level out (or opposite)
2. The more load there is on the battery the more potential for sagging the voltage. This isn't a problem if you stay way under the battery's maximum discharge rate (if you stay a few orders away from it's internal resistance)
3. Different battery technologies have different discharge curves. Some batteries maintain their nominal voltage until almost the end.

You basically have to know your discharge curve and then probably occassionally calibrate if you want accurate readings.
246  Forum 2005-2010 (read only) / Interfacing / Re: Nitgen FIM3040LV Fingerprint reader on: January 24, 2009, 06:28:44 pm
Sure enough, I actually am building something involving that finger print system and the arduino. I actually wrote a whole bunch of code to do a variety of different functions with the Nitgen unit.

Originally I had a little trouble (well, a lot) because I had assumed that the arduino and nitgen units were the same endian. They aren't. They are backwards. That could be a big portion of your problem. Also, the nitgen wants RS232 signalling not TTL so you need something like a MAX232 chip.
247  Forum 2005-2010 (read only) / Interfacing / Re: Any chance serial drops zeros? on: January 18, 2009, 08:26:31 pm
Yeah, drspectro pretty well described the problem. I'm posting only as a bit of trivia. This is a known problem and telco companies have fixed it on their lines. Go here to find out all you never wanted to know about how to fix the problem if you control both ends of the line:

http://en.wikipedia.org/wiki/B8ZS
248  Forum 2005-2010 (read only) / Interfacing / Re: Scott Edwards Mini SSC on: January 20, 2009, 12:02:20 pm
Yes, there is a simple way to test it. RS232 logic is AC. It swings both positive and negative. It also has a larger voltage range, usually around 14V +-. 5V TTL logic swings between 0 and 5V. So using a scope you can view the communication between the current devices to see what the signal looks like. An RS232 signal will have a large swing plus and minus while a TTL level signal will not switch polarity and will have a lower voltage swing.

And, if you do need rs232 signalling then look into a MAX2322 chip (and get 5 capacitors of 1uf) or someone recently posted a little circuit board from Wulfden: http://wulfden.org/TheShoppe/pa/index.shtml
249  Forum 2005-2010 (read only) / Interfacing / Re: Wiring 1P2T Relay on: January 12, 2009, 09:48:38 am
Well, yes certainly you don't want a transistor that could draw more than 40ma through it's base. I'm pretty sure no 1A transistor would though. It's still best to look in the spec sheet to be sure.
250  Forum 2005-2010 (read only) / Interfacing / Re: Wiring 1P2T Relay on: January 11, 2009, 08:19:52 pm
The coil on your relay uses 44.7ma. So it's only barely over the max current capacity of the arduino pins. Still, it is over (and by more than 10%) so it's not a good idea to continue using the relay like that. As anacrocomputer said, a transistor can be used as a current amplifier. A transistor is usually rated way higher than 40ma. 1A transistors are quite common.
251  Forum 2005-2010 (read only) / Interfacing / Re: Wiring 1P2T Relay on: January 10, 2009, 11:51:35 pm
Ok, so, if the bottom looks like this:

__________________
|                             |
|  O O                O   |
|  O O                O   |
|                             |
__________________

And if you count the pins left to right top to bottom (with six pins #'d 1-6) then 2 and 5 are the pins for the 5V coil. 1 and 3 are the normally closed pins. 4 and 6 are the normally open (and closed when the relay triggers) pins.

Note that the wiring above is for a 842. The 842A is apparently different.
252  Forum 2005-2010 (read only) / Interfacing / Re: How to determine current in line ? on: January 08, 2009, 10:29:54 pm
Ah... Well, that IS complicated but it sounds quite nice too! Best of luck, it sounds like it'll be really cool.
253  Forum 2005-2010 (read only) / Interfacing / Re: How to determine current in line ? on: January 08, 2009, 09:57:13 pm
Maybe I just don't understand (wouldn't be the first time...)

You want to have, say, two locations which both turn on the light. And you want to have push buttons at both locations? Do you plan to have arduinos at both locations? RF transmitting between the two? Relay at only one of them?
254  Forum 2005-2010 (read only) / Interfacing / Re: How to determine current in line ? on: January 07, 2009, 09:57:43 am
Personally I think that three way wiring is easier than what you seem to want to do. It might be cool to have push buttons at multiple locations that all toggle the lights. But that's going to be at least as complicated as three way wiring.
255  Forum 2005-2010 (read only) / Interfacing / Re: How to determine current in line ? on: January 04, 2009, 08:18:26 pm
Quote
Hey, I happened to trip over this while Stumbling for arduino articles. I hope it helps.

http://www.glacialwanderer.com/hobbyrobotics/?p=9

That link looks very close to what is being discussed here. Except that we're discussing something a little bit more complicated by using the relay as part of a three way switch assembly. But it's not too much more complicated.
Pages: 1 ... 15 16 [17] 18 19 ... 22