# Tag Info

## Hot answers tagged raspberry-pi

35

If you really want "to understand how computers work on the low level", then it could be argued that neither Arduino nor Raspberry Pi are suitable. Both of these platforms (their hardware and software) are designed specifically to hide the low-level details in order to make it easy for people who don't care about those details to accomplish their higher-...

30

This must be British. For them "fit" means something like what we would call "install". For us, "fit" means how well something fits, meaning how good it is at mechanically going into the right mounting holes or whatever, or how effective it is overall in the role it is being used in. In this case "no-fit" means "do not install". This is often done when a ...

29

Neither: it can be considered a single-board computer where the main CPU is a system-on-chip.

24

What you are trying to do won't really work. First a "C program" doesn't consume a particular amount of power. A particular program performing a particular task on a particular processor may cause a reasonably measurable increase in power draw by that processor, or not. The power draw of a processor will only change significantly if it would otherwise go ...

23

Other common terms used are "no placement" (NP) or "do not place" (DNP) but "no fit" would fall into the same category. It means the circuit board (PCB) has pads where a connector may be placed, but when you receive the board it won't have a connector installed. It will be up to you to source the connector and install it youself if you require it.

21

The user manual of your multimeter tells us why: In the current measuring mode (DC or AC): input impedance approximately 3 kΩ. Which in all honesty is just a joke. So with 5 V the most current you can get is 1.67 mA, but it doesn't even tell us the range of the input impedance, so the value you measured is "fine". It says to be able to ...

18

Trying to do with with IIC is a bad idea. IIC is really meant for communication between chips on a single board. Since the maximum required current to pull a line low is limited, the lines are relatively high impedance (a few kΩ). This means they can pick up noise easily, which is a serious issue when running in unshielded cable in the walls ...

16

Run code on the RaPi without OS: No problem. David Welch has done the grunt work, check his gitub. Basically, you can take the standard startup files and replace the kernel.img with the file you want to run. To avoid the 'SD card dance' you can run a bootloader that receives the image-to-be-run over a serial line. I have added an auto-reboot, so you can run ...

13

The best way to do this would be to use a transistor as a comparator to make the transition sharp. Here is an example circuit: It uses the LDR as the upper part of a voltage divider. When the LDR resistance drops the voltage at the transistor base rises and turns it on. The transistor can be any general purpose NPN. We can calculate the resistor value based ...

13

An Arduino can be used with the Arduino SDE, which provides some functionality in a 'hidden' way, but it can also be used with plain assembler, C, or C++ (and probably with a lot of other languages, but those seem to be less common). There is a wide variety of add-one boards available called shields, is most cases with support software that integrates with ...

13

The idea of the transistors is that: If the Left is low and the right is high R2 (and the left transistor a little) will negative-bias the base of the right transistor's base, allowing it to push the gate to the right voltage; closing the FET's channel and the body diode will block as well. If the right is low and the left is high, the left transistor's b-e ...

13

The industry-standard way of doing this is to use an optically-isolated coupler. The proper industrial method is to use a modular system where you can select a module for mains power input and logic-level output. For example this AC input, 5V logic output module from Opto22: If you were designing your own circuit, you could do an equivalent with an opto-...

13

If safety is a primary concern, rather than build that circuit up, you could consider purchasing a standard AC-input module for about $10-$15. They are UL, CSA, CE, and TÜV safety certified (it's still possible to go wrong and create a dangerous situation, especially if the wiring is sloppy, but less likely). Best to have someone knowledgeable look it over ...

12

The cheapest and simplest solution is just to buy a tiny mains-powered USB charger and wire up the USB +5 and ground lines to detect when the charger is powered by AC.

12

A relay is almost certainly NOT the right tool for the job. The first step in wiretapping an interface in order reverse-engineer it is to determine the nature of the signals you want to look at. For voltage signals, you need a high-impedance buffer amplifier (like the input of an oscilloscope) that will cause minimal disruption to the existing circuit. For ...

11

Choosing the series resistor for an LED: You need to know the forward voltage of your LED (Vf in datasheet) This will vary depending on the colour. For example a typical red LED has a VF of ~2V, a blue LED a Vf of ~3.5V. You then need to decide on the current you wish to run your LED at. It needs to be under the maximum continuous current (Imax) specified ...

11

Are you familiar with shift registers like 74HC595? It requires 3 pins from your RPI and you can control 8 output lines. You can easily cascade them effectively controlling n×8 output lines. Data is serially clocked into the shift register and once all 8 output bits are transferred, you latch the bits onto the outputs. I was about to add the datasheet here,...

10

To eliminate any possibility of surprise, and to generally make things more robust, I'd suggest using an optocoupler like 4N25. simulate this circuit – Schematic created using CircuitLab With this arrangement, you don't need to worry about how to combine the separate grounds of the two systems, because their grounds simply aren't connected. Also, if ...

10

I've been dabbling in electronics since the 1970s and had products used in nationwide broadcasting chains, reviewed (sometimes favourably!) in hi-fi magazines and (possibly soon) headed into orbit, and I would still consider breadboarding a Raspberry Pi a major project. Find a middle ground : take a look at an ARM CORTEX CPU running at 50 or 100 MHz and ...

10

simulate this circuit – Schematic created using CircuitLab Figure 1. Opto-isolated signal detector. An opto-isolator electrically isolates and protects your micro from the AC and eliminates any ground-loop issues. R1 limits the current to about 10 mA rms. D2 provides reverse voltage protection for the opto-LED, D1. D1 will illuminate on positive ...

10

I strongly suggest to reconsider using your circuit in favor of detection without direct connection to mains voltage. Some examples are: Photodiode to detect light Coil-based current transformer to detect current Current transformer with Hall effect sensor to detect current All of the above have the benefit that they do not trigger if your light bulb is ...

9

192/24 for my vinyl rips (iPod only outputs 48/16). The audio quality of vinyl discs is way below 48kHz 16 Bit due to the analogue and mechanic process - the "scratching" of the needle generates a relative high background noise level. I strongly recommend using flash memory technology in a car instead of magnetic platters. While 2.5" notebook HDDs can take ...

9

The input in question is "floating" until the button is pressed, due to its inputs being of very high impedance. You need to add a pull-down resistor to the pushbutton, 10k is commonly used, thus: That way, the Raspberry Pi input sees a false (0 Volts) until the button is pressed, then a true until released.

9

The components on the back of the motor are three capacitors to suppress the contacts, and a diode to protect whatever switched it from a back-emf. If you reverse the polarity without removing the diode, then you will just put the current through the diode not the motor, and possibly either destroy it or damage your power supply, or both. So you need to ...

9

1: Yes, you can do that. Essentially, that's how power supplies work. They can handle multiple parallel networks within their current capacity. As for the heatsink, that depends on the regulator, the current draw, the ambient temperature, how efficient it is, etc. It's not a simple yes or no. 2: The capacitors depend on the regulator as well. Some require ...

9

The Raspberry Pi's seriall port pins on the GPIO header are 3.3 volt logic levels direct from the processor. The processor will likely be damaged if you connect real RS-232 signals to those pins. You will need an RS-232 interface chip (MAX3232 or similar) to invert the RS232 signals, and convert them to 3.3 volt logic levels. Then you should use a ...

9

Your equivalent question is to measure the length of a plank without a measure. You can always eyeball it. The Mic datasheet will provide the current consumption under various conditions, with different peripherals turned on. That's your best bet.

9

using 2 10 ohm resistors Seriously!? That's essentially a dead short for this opamp. Note the datasheet specifies the output voltage swing with no more than 2 kΩ load. You really can't expect it to function properly with two orders of magnitude lower load impedance. You can lift your arm with a 20 pound dumbell in your hand. How well can you do ...

9

The base / emitter junction is a forward biased diode and therefore from base to ground you will see about 0.7 volts when the GPIO is activated. This isn't enough to light your LED (typically 1.8 volts and upwards is what is needed). Connect the resistor and LED directly to the GPIO line and 0 volts.

8

While using a one-shot timer circuit will work, I think an easier solution can be used. Take a look at this circuit. For clarification, "VBAT" is a 12V source that is always on as long as the battery is connected. However, "ACC" is a 12V source that is only on when the ignition is on or the key is set to "accessory." Rather than using a 5V relay just to ...

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