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661  Using Arduino / General Electronics / Re: Sub-zero temperature arduino and capacitors on: October 20, 2013, 01:34:41 am
Is your power source limited?

Buying some nichrome wire wrapping it around the capacitors and then keep  the current flowing 24/7 enough to warm up the caps to thier operational point, it wont take much power either probably less than 100ma to keep them from freezing.
662  Using Arduino / General Electronics / Re: it is 74hc595 pin compatible with SN74LS151N on: October 20, 2013, 01:29:01 am
This is a bit like a door that opens out when you want a door opens inwards.

They both look the same, even do a similar job but in this instance it's wrong
663  Community / Website and Forum / Re: Arduino.cc reboot: feedback and comments on: October 20, 2013, 01:25:59 am
I've been using the new forum on my galaxy s3 just fine...

The ONLY issue (yes i'm using my phone right now) is if i slip and hit the blue part above unread messages, replies etc... the blue part drops down covering those links  smiley-roll-blue

But if careful it works better now on my phone after the "reboot"
664  Using Arduino / Project Guidance / Re: copy a file from server to arduino for classroom automation on: October 20, 2013, 01:11:23 am
Regarding the aircon... that would be an issue.

If no remote or the ability to issue commands via IR does not exist there's another way which will do the job.


http://hackaday.com/2013/10/06/remote-servo-controlled-lightswitch/

The main advantage is that the switch is still accessible by humans, no risk of electricution (unless you work on it live).
665  Using Arduino / Project Guidance / Re: copy a file from server to arduino for classroom automation on: October 20, 2013, 01:06:00 am
Quote
I mean, the  server will just load and update the schedules to the arduino
No, it won't. A server can not push data to a client. A client can only pull data from a server.

A server can if the socket is already established...

Basically your arduino's can connect to a server and wait until instructions are sent... i'm more curious as to where the data is stored and it's own downtime, the alternative is an external server, using GET or POST to deliver information back  and forth over http
666  Using Arduino / Project Guidance / Re: Solar Powered Water Pump with Back up Battery on: October 20, 2013, 12:58:56 am
Buy a suitable pump and measure the current draw...
667  Using Arduino / Project Guidance / Re: Newbie guidance for dslr timelapse controller (use relay or transistor?) on: October 20, 2013, 12:56:45 am
So you are letting around 2 mA flow, which is well within spec for the output pin.
OK, OK, I know it is well within spec.  And I doubt whether the current matters anyway for a relatively short period of time.  Just a matter of "no more than necessary".  If we assume a beta of 100 - which should be really conservative, it can easily switch 200 mA.  If it is switching logic levels in the camera as one would expect, that is immensely more than sufficient.


Presumably that is enough to turn on the transistor (isn't it voltage that turns it on rather than current?).

Eh?  Transistors ("transfer resistors") are current amplifiers.  FETs switch on voltage.


Yes however you can switch voltage on with a transistor (from it's high side)
668  Using Arduino / General Electronics / Re: Breadboard Problems on: October 20, 2013, 12:26:45 am
Is it a plain white breadboard with a bus line at the top and bottom?

If so there's the problem, you'd better off with a wooden breadboard a hammer some nails and wire.  They're awful and threw out 2 of them, the better quality ones have blue / red stripes for power rails
669  Using Arduino / Project Guidance / Re: Regulating voltage and PWM on: October 20, 2013, 12:20:56 am
The voltage will drop and the current will too.

The hall sensor is a good way to maintain speed, since you have feedback as suggested.

A 9v battery sucks, simply not enough current, swap to say aa batteries then you have the option of using a boost circuit snd step up from say 3v (2aa in series) to 9v, vastly superior runtime.
670  Using Arduino / Displays / Re: LCD 16x2 dont work properly on: October 19, 2013, 11:50:49 pm
I've put one of these LCD's through hell (lose connections, having to bend back into place wires on the breadboard) corrupting it,  dropping it once...

Still going fine...  maybe yours is simply faulty...

Question, when it "worked" was it colder/warmer?   failing that - disconnect it all, clean all the contacts and put it back....
671  Using Arduino / General Electronics / Re: Turn a transistor into a solar cell! (Screw it, a phototransistor!) on: October 19, 2013, 11:42:11 pm
You've discovered the secret ingredient of life.  Google search, done "first". More efficient than almost anything else.

I already knew it was possible, just never looked into how....
672  Using Arduino / General Electronics / Re: Turn a transistor into a solar cell! (Screw it, a phototransistor!) on: October 19, 2013, 10:56:36 pm
http://www.coilgun.info/theory/phototransistors.htm

673  Using Arduino / General Electronics / Turn a transistor into a solar cell! (Screw it, a phototransistor!) on: October 19, 2013, 10:54:01 pm
http://rimstar.org/renewnrg/make_solar_cell_using_transistor_2n3055.htm

A solar cell is kinda futile, but exposing the wafer to sunlight produces a voltage, this then could be used as an optoisolator or if you're desperate a very very tiny solar panel.

I started looking because I remembered the story at Bell Labs, they had a chunk of silicon and some junctions had impurities in and by co-incidence he had a desk fan on his desk going, and when he used his oscilloscope  he was detecting wave patterns, fluctuations after a bit of further investigation he worked out the fan blades were blocking light, letting light through as the blades spun....

So I wondered if anyone tried to convert a transistor to a phototransistor, not found much except for what I just posted.
674  Using Arduino / General Electronics / Re: optoisolators. on: October 19, 2013, 10:45:36 pm
A heavy night of drinking does no good for ones brain.

I got it now.... the resistor should be  on the camera's side to limit the current (as it's a direct short to trigger off the camera) sorry for being so slow lol
675  Using Arduino / General Electronics / Re: optoisolators. on: October 19, 2013, 10:41:38 pm
Ahh ok...    I suppose if i cut into the right place on the transistor, i could make my own phototransistor (and have the 3rd base pin D:)




Here's what concerns me..



Notice on the camera circuit, there's a dead short between + and - of the camera circuit, sure the current will be limited by the intensity of the light shining on the detector (making it low) esp with a 270ohm resistor...

But what happens if more current was to flow, is that not a direct short on the camera side?  or is the current just too low to worry?



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