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ante posted:I built an amp for my car, but the left speaker only gives off a buzz. If I touch its filter cap, it starts working again. It seems more likely that you just hosed up the soldering and left an open connection or a partial short, and when you touch it you're giving it just enough force to conduct properly.
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Jan 23, 2010 08:31
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orange lime posted:The actual Arduino language is a lot closer to Java than C. If you were writing code to be burned as hex to the chip, then it would be C. The actual Arduino language is, in fact, C. The header file that gets included adds a lot of macros and there's a decent library of prewritten code, but it's just C compiled by a C compiler.
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Feb 22, 2010 04:29
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Delta-Wye posted:I know you were supposed to enumerate before drawing more than 100mA, but is it actually enforced at the component level? I always assumed you could just say fuckit and draw a half amp if you didn't have any data lines and nothing would actually stop you. Depends on the host controller. Some of them don't really do power management at all, and will gladly supply several amps of power before melting. Others actively manage the power and will only supply 100mA until handshaking with the device for more. Some don't clamp the current draw, but will disconnect the port if too much power is drawn. Edit: A very small number have actual fuses that will blow if too much current is pulled.
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Mar 10, 2010 02:03
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A 555 is not much more than a pair of comparators and a flip-flop. This page has a decent diagram of the internals of a canonical 555 and some discussion of its functionality. As the 555 doesn't do anything clever involving internal trace lengths or microwave effects or the like, you can generally build a hard implementation in whatever manner you like; wirewrap 555s work just fine, for example, and are frequently used in electronics classes as an introduction to IC-based design. Edit: If you're trying to build a silicon 555 yourself and you're having trouble, I can help you with whatever you're having trouble with if you share whatever layout you've got and your process details that you're building with. But there's not really a "trick" or anything to making it work; it's just everyday transistor/resistor/diode/capacitor and whatever traces you need to hook it together without introducing crosstalk or capacitance. Standard debugging techniques apply: If it's not doing anything, check for accidental capacitance between neighboring traces; if it's shorting, check for accidentally introducing features smaller than your minimum feature size; if it's not driving enough power, add a transistor to buffer the current; when in doubt about what's wrong, just make everything bigger and farther apart. It's helpful to build it as if you were using discrete components at first - set aside an area of your chip for each comparator, and an area for the flipflop, and get it working all spread out like that; once that's done, you can work on packing the transistors together and doing routing tricks to meet your space constraints. There shouldn't be much leakage on such a small circuit, so I wouldn't worry much about your power constraints unless you're either really constrained or need to be able to supply a large current; once you get a working 555 you'd expect to be able to shrink down to meet your feature size without breaking functionality, at which point you've done just about all you can do in terms of power. ShoulderDaemon fucked around with this message at 06:26 on Mar 30, 2010 |
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Mar 30, 2010 05:49
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therunningman posted:Does anyone know a source of cheap 1P10T rotary switches? I am having a tough time finding a place that won't charge and arm an a leg per. Digikey has a few in the $5 range; CKN9478-ND, for example.
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Mar 30, 2010 06:34
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therunningman posted:Thanks. I forgot to mention I need panel mount switches though. GH5603-ND, $11.
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Mar 30, 2010 06:41
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Dia de Pikachutos posted:When I'm wiring up an N-channel mosfet to be switched by a logic input from a microcontroller, where should I locate the gate discharge resistor relative to the gate current-limiting resistor? It matters very little, but option 2 ("before") is probably better. Option 1 makes a voltage divider at the gate, which means you can't drive the gate with a full 5V, only 4.high or whatever. If you're using the FET as a switch, then this isn't actually something that's going to matter, but if you were trying to operate in the linear region or something you'd care.
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Jan 29, 2024 02:51
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AlternateNu posted:This may be a dumb question, but where are the capacitors in the circuit? The model MOSFET has a capacitor between gate and source. In a big beefy discrete power FET like the 2905 in Dia de Pikachutos' circuit the capacitance of that might be 1 to 2 nF - enough that it'll generate small but measurable spikes if you're looking at a scope, and if you didn't provide enough bypass capacity on the driver then there is a slim chance you could cause power glitches. So you put a resistor in series with the gate to limit the switching current. Honestly, 270ohm is a lot smaller than I'd expect - typically I see 1K or 10K in that position - but I mostly only ever look at very low speed circuits which are not at all sensitive to switching time - higher gate current means faster switching. Many circuits will omit this resistor entirely and just count on having enough bypass caps to cushion the power rails from the glitch, and let the driver push the FET as fast as it can. The discharge resistor matters even less, as long as it's sufficiently higher than the current-limiting resistor. It's just there so that if you float the output it goes somewhere reasonable instead of letting the FET float into its linear region. It is extremely common to omit this resistor entirely and just assume the driver will never go into a high-impedance state, but if you're driving from a microcontroller then there's probably a nontrivial period of time at startup when you haven't yet configured the port but your power rails are live, so it's not a bad idea, especially if you're driving a big power-hungry load and you really don't want to risk the FET sitting in linear mode - the failure case here is that your load is damaged by being undervolted and/or the FET is damaged by heating up because you didn't design an adequate heatsink for use as an impromptu linear regulator.
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Jan 29, 2024 03:23
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Dia de Pikachutos posted:I mostly included the gate resistor to limit the amount of current the gate draws to avoid burning out the GPIO pin. Would the mosfet discharge back into the microcontroller when it switches or something? Yeah, your uC can both source and sink current through GPIO pins unless they're specifically labeled as open collector or something. You don't need an external pulldown unless you care about the state of that output during startup, programming, or other periods when you don't have software control of the pin. And you aren't gonna burn out a GPIO driver by driving a FET gate unless the FET is, like, measured in inches. Your potential failure is that you pull enough current to cause a momentary brownout. Most uCs will have internal current limiters that make that impossible if you followed the guidelines for bypass capacitors. Other than that, all you're doing is slowing down the edge a little bit, which will serve to reduce RF noise and maybe avoid some ripple in your power rails if you're sensitive to that. Modern uCs are extremely forgiving and while that is a power FET, it's not a big enough power FET to warrant any particularly careful handling in your design.
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Jan 29, 2024 03:49
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| # ¿ May 20, 2024 23:37 |
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TwoDice posted:Ideally sub $500 and bonus points if it's not physically large. I use both https://www.amazon.com/gp/product/B0771N1ZF9/ref=ppx_yo_dt_b_search_asin_title?ie=UTF8&th=1 and https://www.amazon.com/gp/product/B07PWZTNJK/ref=ppx_yo_dt_b_search_asin_title?ie=UTF8&psc=1 and have been basically happy with both. The handheld one is very basic in term of features and capabilities but it's good enough for basic diagnosis when I can't be bothered to carry something over to the real scope.
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Apr 3, 2024 01:47
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