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16  Using Arduino / Microcontrollers / ArduinoBT: upgrade from 168 to 328? on: July 23, 2012, 11:06:00 am
I can't think of any reason why I cannot replace the ATmega168P-AU on a BT board with ATmega328P-AU.  I would flash the 328's bootloader using the Arduino IDE through the ICSP header.  I would use ArduinoISP as the programmer (I have a dedicated Duemilanove set up for this purpose).  Has anyone upgraded an Arduino BT like this successfully, or unsuccessfully?

I apologize if this has been answered, but my search only showed this old, unanswered post:
http://www.arduino.cc/cgi-bin/yabb2/YaBB.pl?num=1286427603

Thanks in advance.

Jim
17  Using Arduino / Installation & Troubleshooting / Re: Why would bootloader get lost on: July 07, 2012, 08:01:04 pm
The reasons I recommended against an LED were

1. Because it would be reverse biased (except for very fast pulses immediately after the DTR toggles) and will not illuminate the way jmosk wanted/expected;

2. The forward voltage is higher than 1N4148 so it won't clamp as close to 5V;

3. I was unsure of the response time.

But....you may very well be right, and it might work just fine if installed with the correct polarity.  And it would be kinda cool if you could actually see a quick flash each time it operated as a clamp.

Jim
18  Using Arduino / Installation & Troubleshooting / Re: Why would bootloader get lost on: July 07, 2012, 05:52:43 pm
Is thre a specific diode that I should place between the 5v and RESET line to prevent this? Could one just use an LED as the diode which would also show that power was present?

I have used 1N4148 because I have a bunch of them.  I think others have used 1N914.  It should be a small signal diode because a fast response time is needed.  An LED won't work.

Here's a link to the thread where the problem was clearly identified:
http://arduino.cc/forum/index.php/topic,64256.0.html

Jim
19  Using Arduino / General Electronics / Re: Reading decimals of milivolts on: July 04, 2012, 09:31:58 pm
You may find something you can use here.  Open source hardware and software built around MCP3424 with CJC.

Jim
20  Using Arduino / Installation & Troubleshooting / Re: Uno Stand-alone boot problem - looking for long term solution on: July 04, 2012, 08:19:38 pm
Too low. Needs to be 7VDC or greater for a 5V board.

Jim
21  Using Arduino / Installation & Troubleshooting / Re: Why would bootloader get lost on: July 04, 2012, 08:18:10 pm
When the Duemilanove (and early Uno's) are automatically reset by jiggling the serial port's DTR line, a high voltage spike will often occur on the processor RESET pin.  I understand that this can put the ATmega into high voltage programming mode and wipeout the bootloader. I've experienced this on several older Uno's.

Solution is addition of a signal diode between +5V and RESET (cathode to +5V).

At worst, this will fix a known issue. At best, it will also solve the problems you are having.

Jim
22  Using Arduino / Installation & Troubleshooting / Re: Uno Stand-alone boot problem - looking for long term solution on: July 04, 2012, 08:01:30 pm
What's the voltage output from the wall wart?

Jim
23  Using Arduino / Programming Questions / Re: How to programatically determine if my Arduino is running from USB power or VIN? on: May 29, 2012, 07:48:30 pm
Quote
PS There is already a voltage divider on the Uno that splits Vin in half.  Look on the Uno schematic at the inputs to LMV358-1.

However half of 12V is still too high for an analog pin.

Agreed.

Jim
24  Using Arduino / Programming Questions / Re: How to programatically determine if my Arduino is running from USB power or VIN? on: May 29, 2012, 07:43:21 pm
Run a flywire from pin 1 of the LMV358 dual op amp to any unused ATmega pin. If HIGH you are running on Vin. If LOW then Vcc is provided by USB or another source.

Just another option.

Jim

PS There is already a voltage divider on the Uno that splits Vin in half.  Look on the Uno schematic at the inputs to LMV358-1.
25  Using Arduino / General Electronics / Re: Help with p-channel mosfet circuit on: May 23, 2012, 06:47:20 am
One of the main reasons to use a microcontroller is that it lets you keep the hardware simple by doing the rest in software. Changing the polarity of an output pin should be a minor change, not a rewrite.

The difficulty would have been modifying existing code to autodetect "old" boards that use the present NPN open collector configuration!  Avoiding this complication is a nice side benefit to going with an arrangement that drives the gate with an nmosfet.

Jim
26  Using Arduino / General Electronics / Re: Help with p-channel mosfet circuit on: May 22, 2012, 11:02:22 pm
Thanks for that information. Very helpful.

I have also learned recently of an IC family that looks like a good option: LMN400 or LMN200 from Diodes incorporated. These devices bundle an n-channel MOSFET (to drive the gate) and PNP to do the heavy lifting.

There are also some other similar load switches that use a p-channel MOSFET in place of the PNP.

Using one of these load switches keeps the polarity of the signal the same as my current config so I wouldn't have to rewrite any code.

Jim
27  Using Arduino / General Electronics / Re: Help with p-channel mosfet circuit on: May 20, 2012, 09:36:14 pm
Thanks, Paul.

Of course, you are absolutely correct about the SSR current demands.  The board hosting this sub-circuit supports a variety of temperature control applications, and I wanted it to have the flexibility to drive larger loads.

The extra complication is there to provide flexibility, even though most SSR's can be driven more easily.  I would still like to at least be able to evaluate a mosfet-based high side switching arrangement, even if in the end it turns out to be something to just file away for a future need.

Jim
28  Using Arduino / General Electronics / Help with p-channel mosfet circuit on: May 20, 2012, 07:20:31 pm
I am considering some new alternatives for a circuit that sends a slow Arduino PWM signal to a SSR which controls an electric heating element. 

Right now, the circuit consists of a low side switch with NPN transistor (2N3904).  That configuration is fine for many situations, but sometimes the output is used for something besides driving a SSR.  In those instances it would be more convenient if the load were tied to ground and the 5V side were switched.

So I am looking at a high side switch instead.  Right now I have the replacement circuit tentatively drawn with a PNP (2N3906) and 1K current limiting resistor between the gate and Arduino pin D10 (see attachment).  (Note, there are obviously two outputs shown in the figure, but I will arrange them both the same).

Would an IRLML5203 p-channel be a suitable replacement for the 2N3906?  As the figure shows, it has to carry max. 200mA.

If I use a p-mosfet, I (think I) know that the current limiting resistor isn't needed between D10 and the gate.  But do I need a pullup to keep the gate high until D10 is done being configured as an input?  Is there any other reason to have a pullup on the gate?

Any suggestions about a more suitable mosfet, and/or circuit configurations would be really appreciated.

Jim

29  Using Arduino / Programming Questions / Re: Using buttons as commands for servo and motor controller, but no response. on: April 27, 2012, 07:39:58 pm
Try this:
Code:
  if ( digitalRead(upA) == LOW ) { .......

Jim
30  Using Arduino / General Electronics / Re: Solder paste for stencils on: April 02, 2012, 07:57:02 am
I've built maybe two dozen boards now with FT232RL using the ChipQuik lead-free syringe from Digikey and Polulu mylar stencil.  The 0805 and SOIC components come out perfect every time.  But the SSOP chip (FT232) almost always has bridges.  The lack of true flatness of the mylar (it is slightly curled) seems to allow the solder to squeeze laterally under the stencil while being squeegy-ed.  The result is too much paste for the component, hence the bridges.

FWIW, I have found it to be quicker and easier to leave the SSOP chip off the board when reflowing, and then manually solder it.  I put down a healthy layer of RMA flux from a pen-type applicator, and then carefully line up the chip with the footprint on the PCB.  Tack two diagonally opposed corners, then sweep a tinned chisel-style tip across all of the pins.  I've used this procedure on 3 boards now with much better results.

Jim
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