Podcast #128: We chat with Kent C Dodds about why he loves React and discuss what life was like in the dark days before Git. Listen now.

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29

I expect this to be a typographical error. They used the wrong picture to illustrate the question. In this case they used the same picture as the one used in question 2-28. The questions 1-36 and 1-37 have good images to identify the pin1 and I assume something similar was intended for the question 1-35. A pdf version of the book is this, and question in ...


26

This question makes no sense. First and foremost: The letters don't identify pins. They appear to identify four separate diagrams, each depicting a separate part! At best, we can imagine that each letter is meant to label one of the two pins on each of four different parts; even then, though, each of those parts would theoretically have a "pin 1". Second: ...


25

It is a mouth-full to say as a full name. I found this description here. hFE is an abbreviation, and it stands for "Hybrid parameter forward current gain, common emitter", and is a measure of the DC gain of a junction transistor. So on a multimeter, it indicates a mode where the meter can measure (probably crudely), the HFE of a transistor. EDIT: ...


24

There's 6 metres of wire. 3 metres to the radio and 3 metres back to the battery. 0.11V/m * 6m is 0.66V which is more than 0.5V. This is one of those questions that's easy to get wrong if you haven't seen it before.


22

I actually prefer vias as testpoints for just the reasons you mentioned. I think it makes using a multimeter or a scope probe much easier. Which, after all, is the main use of testpoints. Where possible/practical, I like to size my vias large enough or use small plated through holes so that 30 gauge wire can easily be soldered in. Then I can clip a scope ...


21

Was an ASIC Design Verification Engineer at Qualcomm. In the most simple way I can explain it: Testing: Making sure a product works, after you've created the product (think QA). Verification: Making sure a product works BEFORE you've created it. They're both testing, just that verification is more complicated because you have to figure out a way to test ...


14

It sounds like these test points were thru hole pads, not necessarily vias. Yes, you can use a thru hole pad as a test point, especially if it is not intended for automated testing. For a technician, a thru hole pad can be convenient. A pad doesn't really add cost except for using space, it is easy to hold a scope probe on it, and you can solder a wire to ...


14

Your layout looks a lot worse in the screen shot than it actually is with the ground pour, however I'd still try to isolate the ground return from the load caps and have it go right back to the ground on the chip. I'd also like to see a ground pour under the caps and crystal (maybe you have one) and connected to the same ground point as the load caps. That'...


13

Drag a scalpel blade along the bit you want to tin, making a bright copper spot, and dip into flux, before inserting into solder blob. The insulation is self-fluxing once it gets up to temperature, but this trick gets copper into contact with hot solder immediately, speeding up the process. Also, arrange a fan to remove the smoke; it contain isocyanates ...


12

Instead I can read about ~1.2V That makes perfect sense as the TIP130 is a Darlington transistor. It has an internal schematic like: Note how between base and emitter there are actually two BE junctions in series, added up those two would have a forward voltage of around 1.2 V. Also note the additional diode between collector and emitter, it is only ...


11

The pins used for making the kind of test fixtures, which the O.P. is describing, are called: contact probes, or spring loaded pins, or pogo pins. They come in various sizes and with various shapes of tips. The choice of a tip depends on the type of test pad: via, flat pad, pin from a throughole component on the solder side. Here's a datasheet of the pogo ...


11

Is there some method that could monitor a device for very long periods of time with millions of packets going by and find the source of the error? Yes. The device is called "USB protocol analyzer". If you monitor only the host software side, the maximum you can see is that there was some "transaction error", and the port can or can't recover after ...


10

Generally in the embedded systems I design, I first try to add as much circuitry as needed to test out the overall system, in addition to the microcontroller itself, without adding extra cost (I might add an diagnostic LED for basic output at a cost of a few cents.) Usually this means using whatever leftover analog channels I have available to poke around ...


10

Instead of having dedicated circuitry that lights a LED for each wire, I'd test the whole thing with a microcontroller. The microcontroller would be capable of driving each line high or low at one end, although small series resistors should be used to prevent damage in case lines of the cable are shorted to each other. At the other end it can apply either ...


10

For me, the simplest way would be this one. For an N-wire cable, get an MCU with at least 2·N available GPIO lines. Connect both ends of your cable to the 2·N lines, like this (where I've used a 3-conductor cable as an example): The N upper lines would be open-drain outputs. The N lower lines would be inputs. For each one of the N wires of your cable, you ...


10

The test board arrangement referred to is commonly known as a Bed-of-Nails board. The pins used are called pogo pins or spring-loaded test probes: (source: eBay) Pogo pins come in a variety of contact shapes: Yes, specific test points, and pogo pins in corresponding locations, would be good - else the pogo pins would simply press against random parts of ...


9

I just saw a great and simple project that does just this: http://www.youtube.com/watch?list=PLFA57ACAC0F0DE0D1&feature=player_detailpage&v=cwiLQWJq2LQ The project is by Alan Yates: http://www.vk2zay.net/ As I understand it, it uses a high impedance gate of a JFET to detect fluctuations in the E-field in the wires due to noise on the mains. The ...


9

If there is room, I like to put real test points (that you can clip an oscilloscope probe to) onto a board for any signals I might want to look at, plus all power rails. You can get them in either through-hole or SMT varieties. Both are around the same price (about 40 cents in single quantities). They can easily be left off (marked DNI/DNP) in production ...


9

Measure the resistance of the fuse. If it's very low (close to 0 ohms), it's still good. If it's very high (open circuit), it's blown. A 200 mA fuse should have a very fine wire visible inside the glass. If it's completely clear, the wire is gone (blown).


9

Continuity testing of an in-circuit component is not a reliable procedure, independent of signal injection and its associated risks. The component leads may be interconnected via other circuit elements, thus giving a false continuity result, where the component itself is actually not a conductive route. Regarding the risks of introducing a voltage through ...


9

As I see, no answer was accepted. Let me offer another answer. Most modern ICs use so-called Pierce Oscillator to generate stable clocks using crystals. Here is the main circuit configuration: As one can see, the circuit is not symmetrical: the right side is output of some driver (usually designated as XO), and the left side is input to an inverting ...


8

"Open Drain" output devices operate like a switch. They don't source current of their own. They are usually used to either drive higher current devices, or to connect to a bus along with lots of other devices. To use as a standard output device you have to supply the output with a voltage. This is in the form of a pull-up resistor (a resistor connected ...


8

The SN74HC266N is CMOS, not TTL, and has open-drain outputs. Try putting a pull-up resistor (1k, say) on the output. You should then get the expected outputs, according to the truth table in the data sheet.


8

You have to apply a high voltage, like +500 V DC via 3 or more series resistors to the central anode, and connect the cathode via a 100 k\$\Omega\$ resistor to ground. The HV supply has only to source less than a mA. If an ionizing particle passes through the GM-tube, it will cause a brief discharge current, which in turn will give a brief pulse over the ...


8

Vias take up space on at least two layers on the board. Test pads take up space on just one.


8

You mention that the oscillator starts when you touch it with tweezers. That indicates to me that maybe you need a bit more capacitance on one or maybe both (depends on how this particular oscillator works) of the pins of the crystal. I'm talking about "(3) load capacitance" in the datasheet. Are there any load capacitors connected to this crystal ? If not I'...


8

The 15 metre band is 21 - 21.45 MHz, so the third harmonic will be above 63 MHz - too high. 10 Metres is 28 - 29.7 MHz, so the second harmonic will be 56 - 59.4MHz - looks like B is the right answer. You have to look at the defined band frequency limits, rather than the frequency calculated from the band name.


7

If you remove the cap you'll have a metal dingus where you can solder a wire to. You then have a test lead which can hook onto wires, IC pins, resistor leads, you name it. Use it to make signal or power connections or as measuring leads to a DMM. They allow for finer work than alligator clips, which serve the same function: It's a good idea to have ...


7

An Oscilloscope and multimeter is standard for electronics work, and not regarded as fancy laboratory equipment. You can pick a second hand analogue scope up on eBay for a few dollars which will make your life a lot easier. To answer the question though, if your signals are audio then one easy way of testing is a small speaker/pair of headphones. If ...


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