SparkFun Forums 

Where electronics enthusiasts find answers.

Search found 194 matches

 Go to advanced search

Re: FETs with built-in pullup/pulldown resistors

 by AndyC_772 ¦  Tue Aug 28, 2012 11:29 am ¦  Forum: SparkFun Product Questions ¦  Topic: FETs with built-in pullup/pulldown resistors ¦  Replies: 8 ¦  Views: 1320

In my experience the cost to buy and place a resistor is as close to free as makes no difference, whether it's 0402, 0603 or 0805. CEM's often don't even bother to bill for the parts themselves, and I can't think of any reason why a good one should need to charge a different amount for an 0402 as a ...

Re: FETs with built-in pullup/pulldown resistors

 by AndyC_772 ¦  Mon Aug 27, 2012 5:19 am ¦  Forum: SparkFun Product Questions ¦  Topic: FETs with built-in pullup/pulldown resistors ¦  Replies: 8 ¦  Views: 1320

What package type gate threshold, Rds(on), current rating and gate capacitance do you need?

Surely you can find room for an 0402 resistor next to the FET?

Re: Programming a SMT PIC microcontroller

 by AndyC_772 ¦  Thu Aug 16, 2012 1:28 pm ¦  Forum: PCB Design Questions ¦  Topic: Programming a SMT PIC microcontroller ¦  Replies: 5 ¦  Views: 1656

Just one device? I'd solder wires to the pins of the chip and connect them to the standard 1x6 header. Program the chip, then desolder the wires once you're done.

Re: Need to store 2 channels of 40kSa/s for <$250

 by AndyC_772 ¦  Mon Aug 13, 2012 12:17 pm ¦  Forum: SparkFun Product Questions ¦  Topic: Need to store 2 channels of 40kSa/s for <$250 ¦  Replies: 8 ¦  Views: 892

I felt much the same about the DSO Quad. It looks like a really nice, cute little piece of kit, and clearly most of the hard work has already been done - but by all accounts the firmware just isn't as complete or reliable as it needs to be. I'd have bought one without a moment's hesitation if it did...

Re: Need to store 2 channels of 40kSa/s for <$250

 by AndyC_772 ¦  Mon Aug 13, 2012 11:04 am ¦  Forum: SparkFun Product Questions ¦  Topic: Need to store 2 channels of 40kSa/s for <$250 ¦  Replies: 8 ¦  Views: 892

I normally like to start any search by finding out what actually exists, then filtering by other criteria afterwards. I'm inclined to suggest that this sounds like quite an important piece of capital equipment, and that there needs to be an adequate budget available to purchase whatever tool is need...

Re: Need to store 2 channels of 40kSa/s for <$250

 by AndyC_772 ¦  Sun Aug 12, 2012 11:57 pm ¦  Forum: SparkFun Product Questions ¦  Topic: Need to store 2 channels of 40kSa/s for <$250 ¦  Replies: 8 ¦  Views: 892

Re: 3.3 & 5V voltage reg OR 5V voltage reg to voltage divide

 by AndyC_772 ¦  Thu Aug 09, 2012 11:09 pm ¦  Forum: PCB Design Questions ¦  Topic: 3.3 & 5V voltage reg OR 5V voltage reg to voltage divider? ¦  Replies: 12 ¦  Views: 3976

You risk poor battery life with this circuit. Another major problem with using a potential divider is that a current flows constantly from top to bottom, regardless of what flows through your actual circuit. This is just wasted power, and it'll drain your battery. Two regulators (or a single dual-ou...

Re: Feasibility of a small run/prototype SMT assembly servic

 by AndyC_772 ¦  Wed Aug 08, 2012 2:38 pm ¦  Forum: PCB Design Questions ¦  Topic: Feasibility of a small run/prototype SMT assembly service ¦  Replies: 4 ¦  Views: 2313

I honestly have no idea what a pick & place machine costs, or how many boards you could have assembled commercially for that much. I'm sure you've done the calculations. I think the overheads will be the biggest issue you face. For your $1, you need to have someone identify the correct part from a b...

Re: Precise Frequency or Period Measurement

 by AndyC_772 ¦  Mon Aug 06, 2012 2:50 pm ¦  Forum: SparkFun Product Questions ¦  Topic: Precise Frequency or Period Measurement ¦  Replies: 3 ¦  Views: 640

I'd consider using a smaller microcontroller to do the display, serial port or other UI, plus a small CPLD to actually do the timing. A device like an Altera Max II CPLD can count at about 200 MHz, and with a small amount of logic it could easily be made to count the period of (say) 10 complete cycl...

Re: Feasibility of a small run/prototype SMT assembly servic

 by AndyC_772 ¦  Mon Aug 06, 2012 12:11 am ¦  Forum: PCB Design Questions ¦  Topic: Feasibility of a small run/prototype SMT assembly service ¦  Replies: 4 ¦  Views: 2313

I think you'll struggle with the setup and component handling. Existing SMT assembly companies are already competitive on reasonable volumes, where the setup costs can be amortised over hundreds, thousands or millions of units. The niche you're looking to fill is for small volumes, where the time ea...

Re: Supercap charging is very slow

 by AndyC_772 ¦  Sun Aug 05, 2012 12:44 am ¦  Forum: SparkFun Product Questions ¦  Topic: Supercap charging is very slow ¦  Replies: 11 ¦  Views: 1461

If you're just driving a microcontroller and LEDs, why use 5V? You might be able to use 2.5V as your supply rail, with much smaller resistors, and the circuit would last twice as long. There's no point stepping up the voltage all the way to 5V, only to drop it all again in a 330R series resistor for...

Re: Supercap charging is very slow

 by AndyC_772 ¦  Sat Aug 04, 2012 10:23 am ¦  Forum: SparkFun Product Questions ¦  Topic: Supercap charging is very slow ¦  Replies: 11 ¦  Views: 1461

You wouldn't even want the cap charging at a rate limited by its 100mOhm ESR. Suppose the available voltage source really is 1.5V, the current into the cap is I=V/R = 1.5 / 0.1 = 15A. (You'll never get that from a little solar panel BTW). The issue to watch is the heating effect, though. P=I^2*R giv...

Re: 40 pads - Stencil?

 by AndyC_772 ¦  Sun Jul 29, 2012 2:23 am ¦  Forum: PCB Design Questions ¦  Topic: 40 pads - Stencil? ¦  Replies: 3 ¦  Views: 772

Personally I'd use a soldering iron for a small number of boards to test them out and make sure they work OK. For 100 boards I'd look at contracting the job out to a manufacturer who has automated equipment, or at least, an experienced operator who can solder by hand quickly and reliably.

Re: AVR Schematic Review

 by AndyC_772 ¦  Sun Jul 29, 2012 2:18 am ¦  Forum: PCB Design Questions ¦  Topic: AVR Schematic Review ¦  Replies: 65 ¦  Views: 8786

Thermals are fine, they're a good idea. You'll struggle to solder the larger components to the board without them. Pin 2 of the IC should be grounded, shouldn't it? Placing the resistors off the edge of the ground plane might help prevent them from picking up noise from it by capacitive coupling, th...

Re: Wall socket integrated usb charger

 by AndyC_772 ¦  Sun Jul 29, 2012 1:22 am ¦  Forum: SparkFun Product Questions ¦  Topic: Wall socket integrated usb charger ¦  Replies: 8 ¦  Views: 874

Any power supply designed to plug into the mains is required to provide isolation between primary and secondary circuits (ie. between the mains supply and any low voltage electronics that it's designed to power). It's one of the most fundamental requirements of EN 60950 (and its international equiva...

  • 1
  • 2
  • 3
  • 4
  • 5
  • 13