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16  Using Arduino / General Electronics / Re: Alternative to reed switches in camera control project on: March 06, 2014, 06:59:32 am
Noob error...   he has no idea what he is talking bout... but to me... he is using this:
17  Using Arduino / General Electronics / Re: Power Supply on: March 03, 2014, 08:42:35 am
Hmmm... I'm just saying what was there... I know these things were cheap... but there were 4 1N4001's in a bridge configuration... I agree that a lot of these things would just use 1 diode with a filter cap.
18  Using Arduino / General Electronics / Re: Power Supply on: March 03, 2014, 06:04:27 am
Having seen the inside of an Atari power supply, I can say... the regulation happened somewhere else.  IN my case, the only parts inside he power block were transformer, 4 diodes and a 1000 uF capacitor.  That will not regulate...
19  Using Arduino / General Electronics / Re: Please explain the circuit. on: March 02, 2014, 08:01:18 pm
An WHY the TIP120?  Because it is about as generic as the 2N2222A and the 2N3904... meaning you can pick one at nearly every Radio Shack retail store...  (or what ever similar store exists where you are)  So you can be assured that not a lot of thought went into selecting the TIP120 other than... it can carry more current than a small signal switching transistor and you can get in your car or on your bike and pick one up "now".
20  Using Arduino / General Electronics / Re: Are shift registers "relatively new" chips ? on: March 02, 2014, 10:59:10 am
It was much more  common in the 70's and 80's to work with 8 and 16 bit wide Data and Address buses, which is why you see those types of IC's getting more focus in the past. The 74x244 74x240 74x373 and similar chips were in nearly every CPU design.  Since they were doing things 8 bits at a time... there was much less of a need to serially shift data unless you were working with a peripheral device such as a Switch array or LED display.   The grunt work was being done with BUS devices.   

21  Using Arduino / General Electronics / Re: Relative newbie to electronics. What's the purpose of the resistor with circuit on: March 02, 2014, 10:52:18 am
You can also make the LED very unhappy that way... and really too bright.
22  Using Arduino / Interfacing w/ Software on the Computer / Re: Communication between arduino uno and mysql database on: March 01, 2014, 10:37:24 pm
I use a python script that receives serial data every 60 seconds from the arduino with 15 comma separated weather data points that python sends to a mysql data base.   It is surprisingly easy and does not require a lot of code on the pc side.
23  Using Arduino / General Electronics / Re: level converter wrong ? on: February 26, 2014, 06:49:23 pm
Do both or any of your I2C slave devices have soldered in pullup resistors on the board?  I had issues with a Gryo I was trying to use that added extra pullup (since I already had some) and it impacted the data transmissions.
24  Using Arduino / General Electronics / Re: Relay LED on, but coil not activating on: February 25, 2014, 12:53:20 pm
Since Sainsmart relay boards use opto-couplers, it is very possible to have a lit LED and no relay closure.  The relay needs it's own power source.
25  Using Arduino / General Electronics / Re: numeric smd digital display on: February 25, 2014, 10:01:37 am
The problem is... there are no "standard" parts when it comes to LED display.  Every manufacturer has the option, and usually selects it, to build the part any way they please with a pinout of their choosing.

This means... the LED display can be multiplexed to save pins... or not and have many pins... none of use can begin to help until these questions have an answer.

If you have a 5V supply and a 330 ohm resistor... you *should* be able to probe  the LED in the package to come up with the manufacturers "layout" for digits 1 -4 and segments A though F.   Then find any old example  on the web... with Google like... for example:

If you look here:
 you might get some ideas about how your part works.

Try it... learn from it... or come back here and ask questions.

But... we are still not able to help you  or send you off in the correct direction... because we do not know what you have... or what you want to do with it.
26  Using Arduino / General Electronics / Re: Smallest DC-DC converter? on: February 25, 2014, 07:25:13 am
I also want to toss a mention here for Polulu.   Their converters are small and perfect for low current conversions (less than 1 amp)
27  Using Arduino / General Electronics / Re: On-by-default P channel MOSFET on: February 25, 2014, 06:56:41 am
The BJT is needed to switch the *required* gate voltage (12V) when a standard MOSFET is used as a power switch.  If a "logic Level"  MOSFET is used then it is likely you can omit the BJT  and replace it with a pulldown since the gate (full on state)  can be reached at 5V  which is what makes it a logic level MOSFET.  (Notice my desire to avoid technical jargon).    A small signal bjt can usually be purchased for less than $0.03 (3 cents) and is "good enough" to solve the problem.   There is *not* huge reason a 2N7000 could not be used in place of the bjt... but they still cost more.

Now, if you *had* a logic level P-Channel mosfet  you would only need a 10K or higher pulldown... unless you still wanted/needed the logic inversion  (1 becomes a 0 and 0 becomes a 1), you would still keep the BJT... or just do the inversion in your code.  Using the BJT in this circuit you have what is called a logic "inverter".  When the arduino pin is Logic "1", the collector is pulled toward GND potential... making the gate voltage low... making the MOSFET turn on.  When the BJT is off, the gate voltage goes high (towards 12V via the pullup resistor) and shuts off the flowing current to the drain pin.  

Note: I feel that the 1K Pullup and 1K pulldown are really too low a resistance value here... making this circuit use more current than needed.
28  Using Arduino / General Electronics / Re: numeric smd digital display on: February 25, 2014, 06:40:53 am
If you call it by the right name, perhaps... "7 Segment LED display", you might actually be able to use Google to find examples but you are going to need to use a less ambiguous name if you want good results.
29  Using Arduino / General Electronics / Re: Arduino High pins supplying less then 5V on: February 13, 2014, 04:27:03 pm
Because the arduino pins employ mosfet push/pull drivers, there is pretty much no way you will get exactly gnd or vcc potential out of a pin. You will have potential loss due to passing through the active transistor at the pin in the chip.  If your mosfet is behaving wildly different with only a small [few millivolt] difference, then i say... you are using the wrong mosfet.
30  Using Arduino / General Electronics / Re: Optimal communication between Arduino and Raspberry Pi on: February 11, 2014, 07:08:43 am
This all implies that somehow your data will get corrupted or "bit slipped" in transit.  That is actually something I have not seen for months with my Arduino connected via USB to a HUB on the Raspberry Pi.  In my case, I just "send the data" as an assembled CSV "string".  No preamble, No checksum.    The only check I do is to verify that the CSV string contains the correct number of "fields".

In this same configuration, the arduino can regularly ask for a "time sync" for the software RTC running on the arduino (so I can show time on the arduino LCD.  When the Arduino sends an ASCII "bell" character, the RPI sends back a serialized timstamp used to synchronise the local clock.

In none of these situations have I needed to add any sort of extra packet overhead while running at 9600.  So, while you could get all fancy with a packet approach, I'm here saying... you don't really need it...  so really, you are doing it because... well, because you can.
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