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586  Using Arduino / Microcontrollers / Re: Looking for a bootloader for the 1284p at 16mhz, anyone know of one? on: February 05, 2012, 09:45:23 am
Correct! The USBTiny cannot program 64+kB Atmels at the moment. They were nice enough to update their web-pages after I contacted them and offered me a $10 gift certificate... A class operation. I doubt you'd get a response like that from some of the e-Bay purveyors of ISP programmers...
587  Using Arduino / Sensors / Question regarding ADC's and SPI on: February 04, 2012, 02:01:05 pm
Hi,
I recently ran across the TI adc122s625 ADC, which seems to be quite ideal for my power measurement application. What I like about it is that it offers 12 bits of resolution, 2 concurrent differential inputs, and very high clock rates on demand (that is, every time you select the chip, it does another conversion, up to about 120ksps at a 4MHz SPI bus speed). The sampling rate can also be controlled by simply turning the CS pin on and off on demand. The ADC is set up for 5VDC operation, so no voltage translators are needed.

The use of a chip with two converters that work concurrently also seems advantageous since it virtually eliminates phase lag on account of the voltage and current being measured consecutively. There likely is still some lag (the coils of the transformer and the current sensor are not the same) but said lag is now minimized from a measurement point of view.

Besides the 12-bit resolution and fast speed, I also really like that I can sample the output from the voltage transformer directly. The current transformer produces a biased signal, but this ADC also has a suggestion re: removing said bias from the input signal in its datasheet. Does anyone have experience with units like this on an Arduino? Are there libraries for similar chips? A search here for the ADC showed no hits...
588  Using Arduino / General Electronics / Re: External power to circuit while programming on: February 03, 2012, 10:40:26 am
would a diode between each potential(!!) voltage source and Vcc do the trick?

Like a BAT 120C, for example? Up to 1A, 0.45V voltage drop at 1A, closer to 0.2V at 100mA. The Atmel chip can operate reliably at 4.5V @ 16MHz, but can the rest of your circuit? I presume that there wouldn't be issues with the FTDI cable either, 4.5-4.9V should be well above the trigger point for on vs. off. At current draws above minimal levels, consider thermal management carefully to keep the schottky dual diode cool.
589  Using Arduino / Project Guidance / Re: 90,000 rpm motor control on: February 03, 2012, 10:30:38 am
Agreed.

One good reason to get the code to compile under Arduino 1.0 is that the serial port is non-blocking. Thus, your control system can presumably work happily away while the buffer is holding any keyboard inputs or the serial port is displaying outputs. I'm thinking of buying a shield like this just for debugging purposes - a inexpensive way to monitor multiple Arduinos communicating with each other.
590  Using Arduino / General Electronics / Re: External power to circuit while programming on: February 03, 2012, 06:37:33 am
I agree that the Leonardo design is the best way to go re: functionality. A micro-USB cable is much more common than a $25 FTDI cable.

That doesn't get you around the issue of USB vs. external power connectivity, however. You could still copy the Uno approach and stipulate 7VDC power supplied or you could us a transistor in conjunction with some sort of logic to detect when an external plug has been inserted into the power receptacle to disable USB power. Many power plugs feature wipers that get moved out of the way during insertion, going from touching one of the contacts to not.
591  Using Arduino / Microcontrollers / Re: aTmega328s so fragile??? on: February 02, 2012, 09:22:20 pm
And it only features a 10 pin head assy as best as I can tell. Maybe the conversion over to a 6-pin head is easy. But I'd look for a 6-pin unit. Plus, being told that the unit in question will be randomly selected from among two (when it is unclear what unit does what) is not exactly heart-warming either.
592  Using Arduino / Project Guidance / Re: 90,000 rpm motor control on: February 02, 2012, 05:22:31 pm
Consider a LCD that sits directly  on the serial port. Then, messages are only a a Serial.print command away. With Arduino 1.0, the serial port is no longer blocking the CPU the way it used to. See Mark Sprouls shield description for what I mean. A similar shield can be bought at Unified Microsystems for $35. But I would prefer Marks shield because it's open source... see if he can sell you a PCB and you then populate it with the components of your choice.

I can't tell what pins the SainShield uses... it's not in the shieldslist either. HTH
593  Using Arduino / General Electronics / Re: External power to circuit while programming on: February 02, 2012, 09:30:35 am
What comes around goes around.  This feature was present on the early Arduino boards.
Yup! I wasn't claiming ownership of that idea... but I like it's rugged simplicity. Hence, I use it in my own board designs. It takes up less room than all the other approaches...

I understand why the Arduino team went the way it did with its current design - it simplifies the device for use by novices. However, it also requires the use of higher-voltage external PSUs (or the switch is not triggered) that then lead to the need of the on-board 7805 to dissipate more heat than I would like. For the boards that I have designed, I have used a mixture of on-board and off-board 5VDC power sources. On-board supplies benefit from a 6VDC external supply and a LDO regulator, minimizing heat inside an enclosure.

One thing I don't quite yet comprehend (and others may be able to help me here) is why the switch inside the external power supply jack cannot be used to detect the presence of an external voltage plug instead of the circuit they chose to use. I suppose that just because a jack is there does not mean that a jack is actually supplying power...
594  Using Arduino / Project Guidance / Re: need more accuracy out of my 60Hz frequency meter on: February 02, 2012, 09:11:26 am
I still think it's easier to use an external RTC to provide a 1s SQW clock signal whose falling or rising edge you can detect easily via an interrupt.

I'd use a smaller pre-scaler on the ADC to speed conversions (you don't need resolution after all) and then detect whenever the voltage curve has gone about halfway above and below the midpoint. That limits jitter. Flip-flop back and forth for a second and you'll know exactly how many times the voltage has shifted from positive to negative. Then divide the results by two and you have your frequency.

If you want to run several seconds to improve accuracy, simply tell the ISR to keep incrementing until you have the right number of seconds in your sample.
595  Using Arduino / General Electronics / Re: External power to circuit while programming on: February 02, 2012, 08:53:26 am
Because that sketch will be coming from a computer connected via USB to the circuit, I would essentially be providing power both from the USB cable, as well as the external PSU, yes?

My suggestion: a three-pin header on a 0.1" spacing with a two pin shunt to jumper two pins at a time. When the time comes to program the thing via FTDI, switch the shunt over to 'program' mode and hence disable access to the PSU power. When in standalone mode, move the shunt back. The center pin provides power to the board, the two outside pins are connected to USB and PSU 5V, respectively. Takes very little room, dirt simple, works every time.

While you might be able to get away with having the computer provide power while the PSU does also, think of all things that might happen if PSU power starts to creep into your computer. Not worth the risk, no matter how cheap the attached CPU.
596  Using Arduino / Microcontrollers / Re: aTmega328s so fragile??? on: February 02, 2012, 08:46:35 am
I mean, I'm as frugal as frugal can be, but the price of "real" programmers has been going down, while the difficulties in using a parallel port have been getting worse...

Ditto. The cost is so low compared to the potential trouble one can get into. However, I would stay away from the Adafruit unit until they resolve their inability to program any Atmel  with more than 64kB of memory. There are other choices out there at very low cost, CrossRoads mentioned a programmer to me (that I have since forgotten) that was a design based on the AVR ISP MKII which sold for less than $20 and which was compatible with 'larger' Atmel chips. If I hadn't already bought my programmer from Atmel, I would have jumped on that unit instead.
597  Topics / Science and Measurement / Re: Any experience with this ADC? PCM1850A PCM1851A on: February 02, 2012, 12:00:44 am
Silly me. I saw the reference to I2S as well but when the datasheet mentioned that the device could be configured using I2C, I thought it might work. I have since realized that while one might be able to configure the unit via I2C (PCM1851A) or SPI (PCM1850A) that the output is still  I2S since there are no registers to query.

Thanks for the help!
598  Topics / Science and Measurement / Any experience with this ADC? PCM1850A PCM1851A on: February 01, 2012, 07:10:42 am
I took a brief interest in this ADC due to its low cost and high performance. For example, it could be really nifty for power measurements since it offers oodles of sampling speed, a built-in PGA, 6 channel MUX for each of the two built-in 24-bit ADCs, etc.) All in a package that has a reasonable cost and which which can be interfaced with easily via I2C.

But the documentation could be better and one aspect in particular has me stumped: Although this is a unipolar ADC design, it does not allow DC inputs. All external pins require a de-coupling pin but there is no differential input as I would have expected. How is this supposed to work?
599  Using Arduino / Sensors / Re: DHT22 accuracy on: February 01, 2012, 06:59:09 am
Not strange at all if there is an element of self-heating going on. How do the temperatures compare?

From what I recall (and memory = leaky) the DHT may be using a resistive humidity sensor that requires (among other things) a 1kHz alternating signal to be applied to it. The resulting output has to be run through an op-amp (or a sensitive ADC) and temperature-compensated. It wouldn't surprise me if this humidity sensor and the thermistor providing the correcting temperature are self-heating at different rates depending on the voltage input. Have you tried blowing a fan across the DHT22?

BTW, I don't think the unit is supposed to be run at 6V.
600  Using Arduino / Microcontrollers / Re: Current Logic Analyzer Choices... on: February 01, 2012, 06:53:35 am
Hi Skyjumper,
If I had a bigger budget, buying 'separates'  would have been the way to go. Sort of like stereo systems... But for now, the QA seems to offer a very nice package and the forums seem to be well-supported also. 
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