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1876  Using Arduino / Project Guidance / Re: NEED HELP WITH TIMER on: February 18, 2013, 05:03:45 pm
so can anyone help with this at all? all these views so far and only one comment?

Define "help" ... if you want it written for you, post in the "Gigs and Collaborations" section. Looks to me like the hobbytronics link contains a big piece of what you want to do. CrossRoads' advice about the current-limiting resistors is well taken, though.

Usually when asking for "help", the expectation is that something has been tried and either needs to be built on or possibly some issue has presented itself, in which case there are good pointers as to how to proceed on the forum here:,148850.0.html (Item 11 in particular)
1877  Development / Other Hardware Development / Re: ICSP in 3v3 target (custom) board on: February 18, 2013, 09:16:23 am
I don't see any worries with your approach. A couple things to watch for (and these are really independent of whether the supply voltage is 5V or 3V3 or something else): If the target board has large loads connected to the µC SPI pins, those can interfere with programming. If it's just a logic-level SPI device, there should be no worries. Second, the SPI device will be exposed to the programming signals which may cause it some confusion, usually nothing that bouncing the power wouldn't fix if it ends up in some weird state, but if it tries to talk to the µC while programming is occurring, that would probably be an issue.
1878  Community / Gigs and Collaborations / Re: Need a small program written on: February 17, 2013, 11:19:42 am
As PaulS said, a 3V output is not the usual thing. If you can tell us what the 3V signal is used for, and how much current is required, then it may be possible to make some suggestions.
1879  Using Arduino / LEDs and Multiplexing / Re: Power supply questions for the Max7219 on: February 16, 2013, 04:13:13 pm
Alright, so the 5v can just be plugged into the Vin port on my arduino Uno? and the same line can also be plugged into the max7219's? then that makes sense. and the arduino will only draw as much current as it needs since I will be using a 5v 1.2 amp transformer. the Led's will draw as much current as they need and the current that is not used will dissipate as heat, in the wall wart? OR thereabouts. OK. the max7219 schematic says that I need two capacitors also, and the internet cant seem to tell me a specific type of capacitor to get. Do I need a specific type? Thanks again! and I moved last July, but I'll always remember the martians!

You've got it now, except that the wall wart will not dissipate "unused" current, it just doesn't supply it. A "5V 1.2A" wall wart is rated to supply 5v at up to 1.2A, or less, depending on the requirements of whatever it is powering. Plugging the wall wart into the wall then leaving the 5V output unconnected will cause the minimum amount of heat to be dissipated. Odds are it's a switch mode supply, so it shouldn't get real hot even under maximum load, but the general tendency will be to heat up more as it supplies more current.

Capacitors are as the datasheet says, a 10µF electrolytic, and a 100nF ceramic. These are exceedingly common, just as a couple examples of a million variations, here are some that I've used, although better prices can probably be found elsewhere:
1880  Using Arduino / LEDs and Multiplexing / Re: Power supply questions for the Max7219 on: February 16, 2013, 03:57:20 pm
there is a 5v pin on the arduino between the GND and 3.3v pins, are you saying that I should connect the 5v pin on the max7219 to that pin? in that case , I would just need to supply all of my power through the arduino, correct? and am I also correct in assuming that I could use the power jack to provide 8v 1 amp of power to the arduino and it should all work? I am unaware of how many amps the 5v pin on the arduino can handle.

Here's the thing. The Arduino has a on-board voltage regulator whose input is connected to the power jack. It requires 7-12V as input, and reduces it to the 5V required by the board itself. The output of the regulator is connected to the 5V pin on the Arduino. (And the input from the power jack is connected to the Vin pin.)

BUT in doing its thing, the regulator dissipates (wastes) as heat the difference between 5V and the input voltage connected to the power jack. How hot it gets depends on (a) how large the voltage difference is, and (b) how much current is being drawn. The amount of power in watts that the regulator needs to dissipate is this voltage difference times the current. The regulator is small and does not have a large heat sink area. Trying to draw an amp through it with a differential of 3V means it will need to dissipate 3W, and that is going to make it very hot. It will likely shut itself down (most regulators have self-protection circuitry), or worst case it could be destroyed.

I thought you had a single 5V wall wart. In which case, as long as it is decently regulated, it can be fed in to the 5V pin, and the power jack left unconnected. And it can also power the 7219s (and hence the LEDs) simultaneously.

OTOH if you have two supplies, one which is 5V and one which is 8V, you could plug the 8V into the Arduino's power jack, and connect the 5v supply to the 7219s, just be sure to connect the grounds between the two. Earlier comment on bypassing still applies. This will require minimal current (~50mA) from the 8V supply, and the 5V supply will provide all the current for the LEDs.

Hope this helps.

OK, and if I split a 1 amp supply parrallely to two circuits, they won't each get .5 amps? because if the current just divides itself equally, I will provide too much current to the arduino. I would need .5 amps to the arduino and about 1 amp to the LEDs. On an unrelated note, I used to live in Goodrich, just south of Grand blanc! small world haha!

No, as CrossRoads said, each circuit will draw its required current. Current and voltage are not independent quantities, they are proportional to each other. The constant of proportionality is called resistance.

Goodrich! That makes you a Martian! Always loved that. When did you move away?
1881  Using Arduino / Project Guidance / Re: internet of things project on: February 16, 2013, 02:42:00 pm
1882  Using Arduino / LEDs and Multiplexing / Re: Power supply questions for the Max7219 on: February 16, 2013, 02:38:25 pm
As long as everything runs on 5V, it can be supplied by one common supply and the current will flow as required. The LEDs are controlled, but not powered, by the Arduino. The MAX7219s actually supply all the current for the LEDs. The SPI interface by which the Arduino communicates to the 7219s consists strictly of logic signals involving very little current or power. So I would not expect the Arduino to consume more than 40mA or 50mA (assuming an Uno) if there are no additional loads connected to it.

Be sure the power supply is able to supply the total current required. It would be good engineering to have some headroom, so I might size the power supply so that it can deliver at least 125% to 150% of the maximum expected load.

Since the LEDs consume a relatively large amount of current, good bypassing is also called for. Check the MAX7219 datasheet, but IIRC, it recommends a 10µF electrolytic in parallel with a 100nF ceramic capacitor on each chip.
1883  Using Arduino / LEDs and Multiplexing / Re: Power supply questions for the Max7219 on: February 16, 2013, 01:42:11 pm
I'm not sure what it means to split a transformer. (I am aware of split windings but assume those would not be accessible in a wall wart even if they are present.)

You are aware that the Arduino can be powered directly from 5V by connecting it to the 5V pin? The single wall wart can do the whole job, assuming it has sufficient current capacity to run everything. The 7-12V input jack is convenient for higher voltage and/or unregulated supplies, but is not the only way to power it. In that scenario, I'm not sure I'd try to draw 600mA through the Arduino's on-board regulator, it would probably get quite warm and maybe even shut itself down.
1884  Using Arduino / Sensors / Re: How to measure the frequency of an ac signal and convert it to a voltage on: February 16, 2013, 10:52:29 am
Try one of the frequency counter sketches, use the measured value to drive a PWM output, and integrate it?
1885  Community / Exhibition / Gallery / Re: First OSH Board and surface mount project. on: February 16, 2013, 10:45:18 am
Nice job, and welcome to the dark purple side!
1886  Using Arduino / Networking, Protocols, and Devices / Re: mesh network between xbee pro s2b on: February 16, 2013, 10:38:44 am
I just shut down my coordinator, and sure enough, the other devices kept working.  Then I shut down one of the other devices (a router) and turned it back on, it couldn't connect.  I let it try while I crawled back up into the attic and turned on the coordinator and the disconnected router hooked up in a few seconds.  There was an end device sleeping and waking up the entire time that kept working just fine through the whole episode.  WTF??

Sorry to make you crawl through the attic smiley-eek  When you say the router couldn't connect after being turned back on, what was the specific symptom? Are JV or NW set to non-default values?

...the network doesn't come back up until the coordinator does...

When is the network considered "up"?

Most of my XBees have an "associated" LED, the meaning of which I misinterpreted for some time. What it doesn't mean is that "I am actively connected to a network and can transmit and receive." Consider a two-node network, a coordinator and a router. Configure them and get them talking. Then power both off. Now power up the router only. The "associated" LED will still blink, indicating that the router is still associated to a network, and when it can again connect to that network, it will then be able to transmit and receive.

What the associated LED does mean is more like "I joined a network (coordinator required for that) and nothing has happened to cause me to leave it." It's just an internal status in the individual module that doesn't necessarily reflect the current ability of the device to actually function on the network.
1887  Using Arduino / Networking, Protocols, and Devices / Re: mesh network between xbee pro s2b on: February 16, 2013, 10:11:48 am
Oh yeah! I just noticed that the mesh network documentation was written by you Jack. Good work! You are a "mesh network" saver!! smiley-lol

And sometimes I'm just a mesh. But glad to help in some small way smiley-grin
1888  Using Arduino / Networking, Protocols, and Devices / Re: mesh network between xbee pro s2b on: February 15, 2013, 09:57:59 pm
When you get ready to add your third XBee, think carefully about where you're going to put the coordinator.  For example if you choose to hook it to a laptop, the network dies (yes, it quits working entirely) when you close the lid on the laptop.

Actually not! The coordinator is only needed for new devices to join the network. The coordinator can go offline and other devices that are already associated to the network keep operating.

Of course this still doesn't make hooking the coordinator to a laptop a good idea! (except maybe for testing purposes)

1889  Using Arduino / Installation & Troubleshooting / Re: Windows 8 incompatibility ? on: February 15, 2013, 07:05:01 pm
The signed drivers have been tested and approved for inclusion in the next releases. The only thing that's new is the cat containing the signature. The driver is still the same old non-included usbser.sys so there's not much to test.
I'd say it's safe to use it.

Like I said, I wouldn't lose any sleep over using it.
1890  Using Arduino / Microcontrollers / Re: Interesting. on: February 15, 2013, 06:10:29 pm
We've come a long way, eh. I read that the ARM6 processor only has about 35K transistors. I've always wondered about the AVRs but haven't found anything very authoritative. With a µC, it'd be nice to see the memory and peripherals broken out.
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