All Questions

8
votes
5answers
2k views

SMD solder now or later?

I'm soldering up some boards with smd parts, using a hot plate to reflow, and I'm (inevitably) realizing that I got some of the wrong parts. Now, is it better to leave the boards with smd components ...
9
votes
5answers
13k views

ATTiny13 — avr-gcc Hello World uses over 100 bytes?

I'm trying to write a program for the ATTiny13. My problem is that it has huge size constraints. Well, when making my first Hello World program, it took 100 bytes of program space just to make a light ...
4
votes
3answers
237 views

What's the max current for this component?

I have a switch marked as having a max current of 2A at 240Vac, and 6A at 125Vac. What would its max current rating be at 12Vdc?
7
votes
4answers
4k views

What's the best bootloader for an embedded Linux board?

I'm designing an embedded Linux board for use as a web-based controller. It will be based around an Atmel AT91SAM9G20, which uses an ARM926EJ-S core. Anyone have particularly good or bad experiences ...
5
votes
1answer
1k views

Old Hall-Effect Keyswitches?

I have a keyboard from an old Silent 700 TTY that I'm trying to bring to life. The problem is that each individual keyswitch appears to be a hall effect sensor. There are no part numbers; the chip ...
4
votes
2answers
2k views

Looking for a Wall Wart Power Supply with an Earth Ground Connection on the Output

I am looking for an AC or DC output wall wart power supply that provides an isolated output and brings out the earth ground connection to the output. Specs -- Either single output or bipolar output ...
5
votes
3answers
5k views

Non-metal cases

This question is really aimed at computer cases, but I suppose it also applies to other PCB cases. Most of the Computer cases I come across are aluminium, or else some other metal; As I understand it ...
9
votes
6answers
3k views

Current Sources - Usage and Projects

I came across this page on building your own current source. What are current sources used for in real-world applications? The only places I've seen them used are textbooks. Do you have any ...
20
votes
8answers
13k views

Cheapest way to add wifi to a project [duplicate]

I need low power wifi for a not-very-data-intensive application. What modules or chipsets should I look at? Other than low cost and low power, I have no restrictions. The cheaper the better. This ...
24
votes
6answers
25k views

Why are Atmel AVRs so popular?

A recent question asked about the advantages/disadvantages of various types of MCU. AVRs seemed not even worth a mention given the answers. Why then does it seem to an outsider that AVRs are ...
6
votes
6answers
996 views

Shielding Techniques for Digital Sensor

What shielding techniques would be best suited for a digital sensor (3 wires - Pwr, Gnd, Sig) in a noisy environment (specifically fluorescent lighting)? Twisted pair (trio in this case) works well ...
7
votes
3answers
2k views

What is the coolest way (using passive cooling only) to step 12V DC down to 5V DC

I'm building a project that needs both 5V and 12V rails which will draw about 1A on the 12V and 0.5A on the 5V. I was thinking of using a 7805 to produce the required 5V but this could generate some ...
8
votes
2answers
480 views

Stencil apertures

When ordering a desktop stencil for laying down solder paste, there is an option to specify the stencil's aperture. Rectangular, home plate, trapezoidal...what's the difference between them? Is ...
6
votes
3answers
2k views

Can I Filter This Split Power Supply?

I've got a battery powered synth that uses two 9v batteries to make a split rail power supply (±9 and ground). I'm trying to use a regular AC-DC power adaptor to replace the batteries. The adaptor ...
10
votes
5answers
2k views

12v LEDs and use on a motorbike

I would like to replace the bulb based tail/brake light and rear indicators/flashers on my bike with one integrated LED unit (flashers in brake light). These are pretty expensive, and since I'm on a ...
3
votes
2answers
584 views

USB-to-UART bridge: protocol mapping?

I was wondering how does the protocol mapping work between the USB side and the UART side when dealing with the Microchip MCP2200? What sort of USB transfer type is used? bulk? isochronous? ...
8
votes
1answer
5k views

XBee short wire antenna replacement to longer wire?

Is it possible to extend the 1mW wire antenna XBees from the short wire antenna, to a longer wire antenna? Will this harm the output stage of the XBee? The point being that I have an XBee in a metal ...
9
votes
3answers
941 views

Should I default to pull-up or pull-down resistor with tact switches?

I understand the basic use of a pull-up or pull-down resistor, including the specific case of using it with a tact switch. When both are an option I was wondering whether I should favor one over the ...
4
votes
1answer
1k views

Using Multiplexer with an Arduino

I am trying to get a Multiplexer to work with the Arduino. Description at sparkfun Datasheet I thought the wiring was pretty simple and as a basic test, I have AREF connected to C1(multiplexer) and a ...
182
votes
17answers
152k views

What is a decoupling capacitor and how do I know if I need one?

What is a decoupling capacitor (or smoothing capacitor as referred to in the link below)? How do I know if I need one and if so, what size and where it needs to go? This question mentions many ...
5
votes
1answer
388 views

Tapping into unused Arduino pins with a shield in place

I am just getting started with Arduino...I figure this is kind of a newbie question but here goes. I have a Duemilanove and the Sparkfun Speakjet shield. I've got some breakaway headers (not the ...
1
vote
1answer
224 views

To receive data wirelessly by 3pi robot

I want to interface a cc2500 module with the 3pi robot...How do i do that...I just have the cc2500 module(the one here) I want my 3pi to move accordingly to the instruction given by another ...
56
votes
8answers
45k views

Decoupling capacitors: what size and how many?

Lots of chips nowadays require smoothing capacitors between VCC and GND for proper function. Given that my projects run at all sorts of different voltage and current levels, I was wondering if anyone ...
5
votes
4answers
6k views

Configuring INA126 Instrumentation Amplifier for Data Acquisition

I have a TI INA126 (datasheet) instrumentation amplifier that I want to use to amplify a noisy, low-level signal from a fabric-based resistive stretch sensor. The resistance ranges for the fabric ...
2
votes
1answer
761 views

Problem programming PIC18F97J60 with PicKit2

I'm having a problem programming a PIC18F97J60 with pk2cmd.exe. Using the same hex file I can program the device fine with MPLAB and the PicKit2 programming utility, but I'd like to be able to program ...
5
votes
7answers
9k views

Zigbee starter kit, any suggestions?

i want to start a home automation project, so finally i choose zigbee as the communication system between the devices. I need something easy to start, so, what do you recomend to buy? there is some ...
19
votes
5answers
4k views

I don't quite understand this FET-BJT preamp circuit

I see this circuit a lot on electret microphone preamps, but I don't quite understand it. The FET is operated as a common source amplifier, so it has gain, inverts, and has relatively high output ...
5
votes
3answers
1k views

Problems with a RFID reader from SparkFun

I am hoping someone here can help me. I am having trouble with a RFID kit I bought from SparkFun. I purchased the USB RFID (SEN-08852) with the RFID Reader ID-12 (SEN-08419) and some RFID cards. ...
4
votes
4answers
474 views

How to find an embedded platform?

A bit of background: We have a system currently in production, but the original programmer passed away, and the current hardware manufacturer cannot find hardware to run the (currently) DOS system, so ...
32
votes
4answers
40k views

How do I connect components when using a circuit board with pads but no traces?

Given a matrix board with soldering pads but no traces, how would you connect adjacent components (including the ends of the jumpers for longer stretches)? Some possibilities I've come up with: ...
5
votes
4answers
3k views

Driving a DC hobby motor using an AVR and a single power supply

I've recently begun experimenting with AVRs and am keen to progress beyond making blinkies to making things move. I've tried to start with something easy, but it seems I'm already foiled! What I'd ...
8
votes
4answers
565 views

JTAG cable and device interchangeability

I see a lot of device specific JTAG cables such as AVR jtag or specific ARM JTAG. Is there any such thing as a 'standard' JTAG cable that will work on multiple devices? I want something that will ...
1
vote
2answers
687 views

How does an LC network filter power?

The ATMEGA datasheet suggests filtering the ADC reference voltage with an LC network, in other words VCC - L - AREF - C - GND. How does the inductor smooth the voltage better than just a capacitor?
6
votes
2answers
3k views

Why is it ok to use polarized caps to remove DC offset from an audio input?

I've seen circuit diagrams that use a polarize electrolytic to remove DC offsets from an input audio signal. The cap is polarized. Why is this ok?
4
votes
7answers
3k views

Vibration sensor (accelerometer?)

For growing crystals it is important that there are no vibrations. Is there a cheap and easy way to measure vibrations in the floor, like people walking, doors closing etc.? Perhaps an accelerometer ...
9
votes
2answers
5k views

Driving a servo with MOSFET

I am trying to build a small battery powered device containing a servo. I would like to be able to turn off the servo to save battery life. I have read previously that MOSFETs can be used to do this, ...
2
votes
3answers
1k views

I2C 7seg driver

Does anyone know of any good I2C 7segment display drivers. I swear a previous answer referenced a chip for this on chiphacker but I cannot find it. I would also be happy with SPI, but I I2C would ...
8
votes
5answers
4k views

RC circuit understandings

I am trying to understand the principles of a RC charging / discharging circuit however I'm at loss regarding certain aspects of its operation. I have a square wave generator giving 0v to 5V levels ...
11
votes
6answers
6k views

Inductive Charging

I've build a small three wheel robot with an Arduino Mega to drive the thing. I'm looking to keep this bot mobile as much as I can without needing to interact with it for charging etc. For the moment ...
11
votes
4answers
6k views

Good filter design software for Mac OS X/Unix?

I need to implement a simple lowpass filter for a data acquisition circuit (using stretch conductive fabric as a resistive sensor). Various sources have recommended that the best way to go about this ...
15
votes
5answers
2k views

Are varicaps (capacity diodes) obsolete?

I have read that varicaps (capacity diodes) are a "modern" alternative to variable capacitors. In several electronics books only positive properties of varicaps are mentioned. But several major ...
3
votes
1answer
234 views

Detecting opens/shorts when driving coils

Using software while PWMing a coil with feedback going to an A/D input, 1) how can you detect a state where the coil is an open circuit? 2) how can you detect a state where the coil is a short ...
4
votes
3answers
3k views

Tips on using a Prototype PCB

Recently I have been trying to get myself an arduino made by hand (as where I live the original one costs about 10x and its fun to make things on your own). I made a compatible on the breadboard and ...
9
votes
1answer
820 views

eBook Reader for Datasheets [closed]

I hate reading datasheets or user manuals on the screen, and printing such documents tends to waste a lot of paper/ink. Has anyone tried to use an eBook Reader for this purpose? Are they good enough ...
2
votes
5answers
773 views

USB Host device

I am looking at creating a USB host devices to talk to a standalone printer. Basically my devices would feed out commands to the USB chip and the pritner would print it without interaction of a PC. ...
2
votes
1answer
1k views

RFID Reader UART

Was wondering if someone could give me a hand with a project that I am undertaking. I have searched forums high and low and am yet to find the information to solve my problems. Basically I have an ...
8
votes
3answers
928 views

Does the frequency of a crystal influence its height?

Here is a picture of two crystals: Does the difference of frequency explain why the 6 MHz crystal on the right has a lower profile than the 5 MHz one ?
11
votes
4answers
1k views

Plastic enclosure for small product [closed]

I have a small hw product and I would like to find a plastic enclosure company that do small runs. Recommendations with experience please (i.e. not a simple Google Search result dump!)
5
votes
2answers
647 views

Embedded PC with Gigabit Ethernet and SD card interface? [closed]

Where do I find such a module? All of the embedded PC modules I've seen so far have only a slow 10/100 Mbit/s Ethernet interface. This is for a scanner application. I get incoming data at a rate of 2 ...
5
votes
3answers
3k views

H-Bridges and Motor Stall Current

How do I determine how powerful an H-Bridge I need to control a DC-motor? In particular, does an H-Bridge need to be able to supply the full amount of current a motor will use when stalled, or would ...

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