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1  Using Arduino / General Electronics / Re: Resistor required for PN2222A transistor base? Diode also? on: October 01, 2014, 09:21:46 am
Yeah mosfets in parallel maybe...   BJT's in parallel... not so good without some extra measures to prevent a runaway...
2  Using Arduino / General Electronics / Re: Resistor required for PN2222A transistor base? Diode also? on: October 01, 2014, 09:17:15 am
I never understand why we must make the 2N2222A supply anywhere near it;s MAX ratings of 800mA... seems to be a sticking point for some.   With 5mA at the base of  a 2N2222A it's  turned *on* enough to drive an LED, a small motor or a standard PCB relay with no issues and come nowhere near hurting a GPIO pin.

To each his own I guess.
3  Using Arduino / General Electronics / Re: Please help with TIP42 control circuit on: September 30, 2014, 07:51:14 am
I can't get it to turn off. I know its an issue with resistor values just not sure where the problem lies.

... sort of implies that was attempted at least.
4  Using Arduino / General Electronics / Re: Resistor required for PN2222A transistor base? Diode also? on: September 30, 2014, 07:07:00 am
I'm having a bit of an issue with the statement:
only there to stop too many amps coming out of the Arduino pin

That is not the *only* reason that you need to place a resistor at the base of a transistor when using it as a driver.  Please try and control your urge to oversimplify your advice.  This is how *bad* Instructables pages get started.

I have no issue with the statement that the value of the resistor is not critical, as long as it is between say 680 ohms and 4.7K ohms.  I consider those to be extremes and as you might see in many many examples... a 1K resistor is just about right as a "generic" value.
5  Using Arduino / General Electronics / Re: 12v input to 7805 voltage regulator heating in a second?? on: September 22, 2014, 08:00:31 pm
High heat is pretty normal for a 7805 with 12V on the input pin if you opted to not use a heatsink.  Just saying.
6  Using Arduino / General Electronics / Re: Battery Monitoring System for Arduino on: September 19, 2014, 07:37:10 am
I solved this concern when I attached a 7.2V LIPO to my LC meter project...

For reference:

I incorporated a Kingmax 500mA 7.2V Lipo with the Polulu power switch to power my portable bench meter.  Adding a resistor divider network in front of the Analog input pin I was able to measure battery voltage.  When it gets too low, the Arduino will send a shutdown command to the Polulu switch.



7  Using Arduino / General Electronics / Re: givinig 5v power for controlling Relays on: September 03, 2014, 08:23:24 am
Typical Relay Driver
8  Using Arduino / General Electronics / Re: Relay Chatter on: September 02, 2014, 06:18:57 am

"A Optically Isolated 8 Channel 5V Relay Module",  where the optical isolation is on the *low voltage, mechanically isolated actuator side,  is not much different than buying snake oil in the wild west period of the 1800's USA.  The term "snake oil" is for any product with questionable or unverifiable quality or benefit.

If you want to do high voltage (AC mains switching)  silently, then you buy a Solid State Relay.  If you do it with a mechanical relay, you will always get noise when the coil side activates the "isolated"  switching arm to move the relay contacts.

Here is a simple and perfectly fine relay circuit... notice it does NOT have an optical isolator and it does not need one.  The power supply of the relay needs to match the voltage of the relay coil.  Proper isolation of the relay voltage occurs with just the transistor by itself.

9  Using Arduino / General Electronics / Re: Moisture sensors reading very low values on: August 27, 2014, 07:51:02 am
Or, as many implementations of this kind has used... move to using an AC signal.

This post may be useful...,22250.0.html
10  Using Arduino / General Electronics / Re: Auto-Power on/off circuit on: August 27, 2014, 07:00:46 am

You simply buy one of these:

It allows you to use a pin to "shutdown" on command.

This is exactly how I created an auto-shut-off option on my LC meter.

If you are still feeling creative and want to build your own... check this out:
11  Using Arduino / General Electronics / Re: I need help selecting a transistor on: August 19, 2014, 03:30:58 pm
And.... sadly, the schematic is sort of wrong.  You do not put the current limiting resistors on the common display pins, you place the resistors on the individual  display 'segment" pins.  If you don't do this, when you have only 2 segments lit to display a "1", each led gets gets 1/2 the current from R and if you display an "8", all segments... each only gets an 8th of the current.  So, with 330 ohms, and displaying a "1" each led gets ~5mA..  With an '8'  on the LED each gets ~1mA.

And then you will be coming here and saying... why are my LED's so dim?
12  Using Arduino / General Electronics / Re: Will this work correctly? on: August 16, 2014, 07:06:15 am
13  Using Arduino / General Electronics / Re: Will this work correctly? on: August 16, 2014, 05:23:00 am
First point:  Resistors have a purpose.  Please try to begin to understand why they exist and why they get used in designs.  And when doing a drawing... if you used them, don't omit them.

If your optocoupler still works (the LEDS are not fried) they may be hope in getting this to work.

Problem #1:

The photosensor (based on my understanding of them) is basically an an open collector NPN output.  It can only pull to GND or be open-circuit.   So, you correctly have the collector from the sensor going to cathode pf the internal LED.  What is missing is a 220 Ohm resistor between the anode side 5V supply.

Problem #2:

The sensor is open collector (meaning very versatile) and this means that I fail to see why you needed an optocoupler there at all.  If you have placed a 10K resistor from the sensor NPN output to +5v you would have a TTL Logic (and therefore arduino pin) compatible level change... You would see logic state changes correctly

Problem #3:

If you want to use an opto-coupler, they usually have open collector npn outputs.  (just like your sensor)  The same solution applies... Tie the collector (output) pin to 5V through a 10K pullup resistor... then attach the collector to a digital pin for state sensing.  When the internal LED is not lit, the mega will see +5V or logic "1" , when the internal LED is lit, the mega will see a logic "0".

So, please explain why you have an opto coupler here because I feel some important information has been skipped.
14  Using Arduino / General Electronics / Re: Edging your DIY PCBs on: August 11, 2014, 07:27:22 pm
I do 1  or 2 passes on a stone wheel grinder.
15  Using Arduino / General Electronics / Re: Protecting diy pcb boards.... on: August 11, 2014, 05:43:46 am
I use the rub-on Silver coating "Cool-Amp" in combination with a clear coat lacquer sprayed "before" soldering.  The Lacquer melts  away while soldering and you end up with a protected board that won't look ugly due to tarnish.  Personal experience is that it takes a long time for the Cool-Amp to actually show tarnish even when not painted over with clear coat.

The product for silver plating copper may seem expensive, but I have had mine for nearly 10 years and have only used about 10% of what is on the jar.
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