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 586 Using Arduino / General Electronics / Re: Working out how to power a project on: March 13, 2013, 01:56:33 pm You're welcome...Careful of how hot those 78XX's get.... if it's getting towards too hot to touch, you'll need a heatsink. (Edit... I mean an external one, not the silver back of the 7805)I tested one this last weekend.... with 12V in and 5V out at 500mA, and measuring it with my Fluke's thermocouple, it got to 110C in seconds before I turned it off, un-heatsunk. With a heatsink it sat at about 40C.And that's why those things are inefficient. Their design dictates that whatever current you draw on the low side, is the same as on the high side. Now, power = volts x current. So Powerin = Voltsin x current and Powerout = Voltsout x current. Rearrange that and Powerin - Powerout = ( Voltsin - Voltsout ) x Current. That difference in power is dissipated as heat, and you have to get it away from the device somehow.That would mean for example, as in my test, if you happen to use 12v to get 5v, you're losing 7v x current in heat, and that's more than the power you're actually using at 5v.
 587 Using Arduino / General Electronics / Re: Working out how to power a project on: March 13, 2013, 01:32:03 pm Quoteleft pin = input current, middle pin = ground, right hand pin = output voltage. Is that right?Yeah, except it's input voltage....Remember the input has to be at least 2 more than the output.Btw you might find this datasheet catalog site useful.... type 7805 in and you'll find a bunch of sheets from various makers. The 78xx comes in various output voltages as you'll see.
 588 Using Arduino / General Electronics / Re: Working out how to power a project on: March 13, 2013, 01:16:07 pm Well if it's a 7805, you put >7v to the left hand pin, and ground to the middle. Then you get 5v out the right hand pin, also using the middle pin as ground......but not all regulators are 78xx so have a look at its markings to see what it is.
 589 Using Arduino / General Electronics / Re: Working out how to power a project on: March 13, 2013, 12:58:08 pm You would probably want to search for Voltage Regulators on the various vendor sites.Simplest, but inefficient for reasons we needn't go into here, is a 7805. It converts an input voltage higher than 5, to 5. But it has a so-called drop-out voltage of 2 (which it basically loses) and which coincidentally for you, means the input needs to be 7 or more, to get 5 out. So, you hook your 7v to the motors; you also hook it to the 7805, then take the 7805's 5v to your sensors. They supply 1A, although I think some makes are up to 1.5
 590 Using Arduino / General Electronics / Re: Working out how to power a project on: March 13, 2013, 12:42:17 pm QuoteDoes this mean that as long as I get the volts right, i can use as much amperage without fear of damaging anything (so 10A for a 1A component say) as it will only draw the amount it needs?Yep, you don't push current, just as pwillard said: a component draws the current it needs. If a 5v motor draws 800mA, but your supply is 5v with a capability of 2A, you're good.... you just spent too many \$\$\$.But if you get a 12V supply for that 5V motor, you'll smoke it.
 591 Using Arduino / General Electronics / Re: Working out how to power a project on: March 13, 2013, 12:23:46 pm Quote I feel like the volts don't matterThey are the thing that matters. Voltage is often explained as being analogous to pressure in a water system: too much pressure and the pipe bursts. Too much voltage and you'll damage the components. Check the datasheet or label of a component and it should tell you what the voltage limits are and what the current draw is likely to be.Say a motor's datasheet says 4-6V, 200mA (800mA peak).... First you need to look for a supply of between 4 and 6 volts: below 4 and the motor won't spin, over 6 and it'll smoke. Then check that power supply with the right voltage, to see if it can supply 800mA comfortably.. So a 5V, 1A wall wart will be good.But also think of this.... if you want to hook up two of those motors to the same supply, you don't need to double the voltage supplied but you do need to double the available current... so you would still be ok with a 5V wall wart, but would need to look for a 2A one.
 592 Using Arduino / Project Guidance / Re: Using a three-way toggle switch for power and digital input on: March 13, 2013, 08:38:23 am QuoteI assume this is the type of switch JimpboZA suggested Ummm, much as I'd like to take the credit, I didn't suggest a thing!
 593 Using Arduino / Project Guidance / Re: Pendulum Balance Robot on: March 13, 2013, 08:08:32 am QuoteGives a page of 0'sIt will, it never changes in that codeQuoteI'm unsure how to measure mWhat is m in the first place?
 594 Using Arduino / Programming Questions / Re: CODE TO CHECK RTC TIME VAYING OR NOT on: March 13, 2013, 07:49:27 am Noted
 595 Using Arduino / Project Guidance / Re: Using a three-way toggle switch for power and digital input on: March 13, 2013, 07:46:36 am Quotebut could I interrupt the ground connection from the Arduino to the battery with the switch, joining each pin to ground and the left and right ones to a digital pin for input? I can't quite visualise that, maybe you should post a diagram.  Won't you still be putting 9v to the digital pins?- although as a I say, I can't picture it.
 596 Using Arduino / Project Guidance / Re: Pendulum Balance Robot on: March 13, 2013, 07:34:48 am QuoteCurrently when the code is ran,  nothig happensDo you mean that literally?- not even the serial write from setup()?Edit.... seems HM and I on the same track here...
 597 Using Arduino / Programming Questions / Re: Servo Motor timed reaction on: March 13, 2013, 07:01:18 am QuoteIs the code right?I'm not being funny, but why don't you try it... then you'll know the answer. If it's not right, be it compile errors or "unexpected" behaviour, then you'll need to do some debugging. If it still gives problems, then ask specific questions here.
 598 Using Arduino / Project Guidance / Re: School project help on: March 13, 2013, 04:45:30 am Assuming you've done these basic tutorials, have a look at this one which explains how to read a light dependent resistor, and this one which covers motors, including direction.You'll also need to think about limit switches to switch the motors off at the end of their travel...  one of those basic tutorials explains how to read a switch.Then you'll need to ponder how to get all of that hung together....
 599 Using Arduino / General Electronics / Re: What Arduino ground pin to wire to existing circuitry on: March 13, 2013, 04:25:03 am As far as I know, "ground is ground" and they're all connected together anyway... you could check that easy enough with your meter.
 600 Using Arduino / General Electronics / Re: How to estimate number of hours remaining before battery dies? on: March 13, 2013, 04:18:40 am QuoteHave you noticed how wrong your laptop or tablet gets this.I think half the trouble is how they estimate the upcoming use. The might have a good handle on Ah left (but I wouldn't know if they do or not) but they seem to take the instantaneous consumption and assume you'll be doing that non-stop until it dies. So if it looks like you have a long time left, as soon as you do something intensive for a few moments, your time left drops drastically based on that heavy load.
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