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    Wireless mouse internal antenna length - crucial?

    Hello. I accidentally broke the antenna inside my wireless mouse -- at least I'm pretty sure it's an antenna. It's about 0.5mm diameter and runs ~115mm around the perimeter of the top of the PCB, then is soldered through on both ends. About 1-2mm broke off, and I thought I'd fix it by...
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    [SOLVED] Okay to connect in-circuit programmer and COM port to PIC at the same time?

    Hello. I'm learning to use the UART/USART on a PIC microcontroller, to interface with a computer for the first time. Every time I want to re-program the PIC, this is what I do: Disconnect COM port from breadboard. Connect Pickit 3 USB programmer to the PIC. Program PIC. Disconnect programmer...
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    PIR motion sensor - analog output - should I limit output current?

    Hello. I bought a PIR motion sensor with analog output (Panasonic AMN22112). Datasheet: https://media.digikey.com/pdf/Data%20Sheets/Panasonic%20Electric%20Works%20PDFs/AMN%20Design%20Manual.pdf Digi-Key page: https://www.digikey.com/product-detail/en/AMN22112/255-1806-ND/735389 The datasheet...
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    [SOLVED] Does current rating of wire double at 50 percent PWM duty cycle?

    Hello. Can you run twice the rated current through a wire if the signal is a PWM at 50%?
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    Hitachi HD44780 LCD - I unplug Vdd but LCD stays on?

    I'm working on a project controlling an HD44780 LCD with a PIC microcontroller. The data lines on the LCD get fed from a 74HC164 shift register that if controlled by the PIC. I had it running, but wanted to keep the LCD off until the shift register has a known value, so I unplugged Vdd on the...
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    Solder iron tip -- is it okay to not insert all the way into iron?

    I've seen two kinds of soldering iron tip: 1) short tip with threads that screw into the iron. 2) long tip that slides all way into the iron, and is held by a set screw. My question is about 2): Would it be okay to run the iron with the tip only inserted half-way into the iron? I'm asking...
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    Record audio above human hearing frequency-- how?

    Hello, I need to build a circuit that can record audio frequencies up to 45kHz. I have two main questions: 1) What kind of microphone do i need? 2) What kind of circuit do I need in order to make these sounds audible to a human? A circuit that can lower the input frequencies by about 20kHz...
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    Smoke alarm -- low battery beep -- timed how?

    Hello. Can anyone please tell me what the typical circuit or mechanism is that times the beep that a smoke alarm makes when the battery is getting low? And say the battery is getting _really_ low -- how much might that effect the timing? For instance -- if the timer is supposed to beep every 30...
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    [SOLVED] MicroSD (or SD card) - through hole connector??

    Hello. I'm trying to find a MicroSD card connector to use on perfboard, but it seems that they are all surface mount. Can anyone point me to a through-hole MicroSD card connector? If not, how about a through-hole SD card connector? (EDIT: changed "protoboard" to "perfboard")
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    [SOLVED] Transistor as audio amplifier - no negative supply needed?

    Noob question here... I've seen some audio amplifiers that use a standard BJT as the amp (example attached). I'm wondering how this can work without a negative voltage supply. I thought audio had to go above and below zero volts? I guess it works, but are there common problems with such a...
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    ESR meter - DIY - what do you think of this one?

    Hello. I want to build this simple ESR meter. I was wondering what you guys think of it. https://electronics-diy.com/electronic_schematic.php?id=948 I especially wonder about it running at only 2.3kHz. Aren't we supposed to test capacitor ESR at around 100kHz? Would it be okay/necessary to...
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    [SOLVED] Sense resistor's power dissipation in a constant current source?

    Hello. I have built a constant current source, and I'm trying to figure out how to calculate the power dissipated by the sense resistor at various currents. I know how to do this for a voltage source, but i am perplexed as far as a current source....? The circuit...
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    Low voltage cut off -- help please.

    Hello. I'm trying to build a low-voltage cut off circuit. The idea is a momentary switch turns on a transistor which powers the circuit, some (unknown) component in the circuit will instantly begin powering the base of the transistor. When a certain low voltage is reached this unknown component...
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    TL431/LM431 - sharp turn-on characteristics?

    Hello. The TL431 and LM431 datatsheets say: "Due to the sharp turn-on characteristics this device is an excellent replacement for many zener diode applications." What is "sharp turn-on characteristics"?
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    Multimeter hold function - broken - possible fixes?

    Hello. I have a multimeter (Mastech 390-545) that has a hold button. The button operates mechanically. The hold function does not work. Once the hold button is pressed, the least significant number just slowly counts up (about 27 times per minute), and no connections/disconnections (once hold...
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    [SOLVED] Ohm's law -- current through a battery -- does battery voltage slow the current?

    amps = volts / ohms So... 1V into a 1 ohm resistance will flow at 1 amp. But what if the 1 ohm resistance is a battery? For example -- a 0.5V battery. With the positive of the 1V power source connected to the positive of battery. Will the battery voltage in opposition to the power source...
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    Transistor to switch on and off op amp?

    Hello. I've built a constant current source based on an LM324 op amp. (schematic attached) I'm trying to turn on and off the LM324 with a transistor (T1). What I expect is when i cut off power to the base of T1, the output of the LM324 (pin 1) becomes 0V, but the voltage actually goes up...
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    EMP (electro-magnetic pulse) - circuits that would be valuable after an EMP attack

    Hello. What circuits do you think might be in high demand in a post-EMP world? I was thinking: --radios --voltage regulators (for charging batteries). --constant current sources (for charging batteries). --???? Please suggest any other circuits you can think of. Especially things that you wont...
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    EMP (electro-magnetic pulse) - post EMP comunication radio -- simple circuit?

    I know very little about radio communication circuitry, but after reading a book about what my country would be like after an EMP attack (or giant solar ejection), I want to build a radio NOW, and put it in a faraday cage. Can anyone direct me to, or draw a simple (hopefully cheap) schematic...
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    Desoldering iron and replacement tips -- mix Radio Shack with Parts Express brands

    I recently bought a desoldering iron from Parts Express (PE) -- model J-045-DS. Then I bought a replacement tip at Radio Shack (RS). I just wanted to tell you guys that the parts do work together, but there is one thing to note: The threaded part on the tip that came with my PE desoldering iron...

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