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.

Hot answers tagged

8

The official schematics show that: PP1 and PP2 are 5V input from USB PP35 is 5V after the polyfuse PP7 is 5V after the input circuit PP3 through PP6 are GND They are to be found on the bottom side of the PCB near the Micro USB (power in) connector (that is on the top side of course).


8

There's not quite enough information in your question to give a definitive answer, but let's go through the design steps so that not only can you figure out this one, but you might be better equipped to solve the next transistor question that occurs to you. Ohm's law Ohm's law expresses the relationship among resistance (R), current (I) and voltage (V): V ...


7

No. Take it on the bright side. You have learned one thing never to do to a Raspberry Pi.


5

Powerbanks are not made for powering electronics. They are made for re-charging batteries. This is important because these two tasks have some requirements that are at odds. Most significantly, in powering electronics it necessary for the supply to be responsive to rapid fluctuations in current draw, but the exact opposite is true with regard to ...


5

Welcome to the Raspberry Pi SE site! Your question may be judged as off-topic for this site (not saying it will, but it may be), but personally, I'm happy that you've asked it. I say that only because radio applications for the RPi don't seem to get a lot of coverage here - which suggests to me that folks are missing out on one of the best application areas ...


5

There is nothing wrong with the GPIO, it just can't supply enough current for your coil. If the coil has just 24Ω, at a 3,3V the GPIO would need to supply 137mA. This source at raspberrypi.org says that the maximum current it 51mA for all GPIOs together and 16mA per GPIO. You can connect the GPIO to a transistor that can supply the necessary 137mA.


4

The statements "220V power" and "I'm very new with electronics" raise concerns. The only responsible advice I can give to anyone who isn't a licensed electical contractor is DON'T. Try something involving lower voltages first.


4

There are no formal published data, but the following summarises what I have been able to discover. Electrical Specifications of GPIO I would NOT apply 3.6V to a GPIO pin, but if the voltage does not exceed Vcc + diode voltage (~0.7V) damage is unlikely. I would use a serial resistor in any event. If you know the voltage may be excessive use a resistive ...


4

Short answer: no way. Long answer: USB ports can only output 5 Volts. It's true that your screen came with (citing the product page you linked) 1 * USB to 3.5 DC Power Cable but that cable is useless for a 12-Volt device like your screen. To me, it looks like they threw the cable in just to "complete" their offering someway, without paying any ...


4

Those resistors are in fact too high. Section 4.1 "Analog Inputs" (p. 17) and figures 4-1 and 4-2 (p. 18) of the datasheet are of special interest: For the A/D converter to meet specification, the charge holding capacitor (CSAMPLE) must be given enough time to acquire a 10-bit accurate voltage level during the 1.5 clock cycle sampling ...


4

I use buck converters that convert 12VDC to 5VDC to power most of my raspberry pi computers. There are many available but be sure to check the amperage output. Most come with a USB A 5VDC output and that way you can use the microUSB for power thus having fuse protection My RPi Zero computers for my weather station as well as my RPi3B+ camera are all ...


3

The subject of ADC error is both wide and deep. Engineers have built careers on studying, quantifying, measuring and resolving ADC error. If you "Google" terms such as adc error analysis, or adc error correction, you'll find enough highly technical and/or scholarly information to keep you occupied for quite some time - for example. But the bottom line is ...


3

Thanks to @Ghanima's great answer I made markings on those +5V points:


3

Adding a resistor in series will not drop the voltage. It will simply reduce the current. Fortunately you seem to have limited the current to a level which the Pi's GPIO protection circuitry can handle. However you are risking destroying the Pi when you connect any voltage more than 3V3 to a GPIO. One way to produce a safe voltage for the Pi GPIO is to ...


3

Yes, (in general) in this case you should wire the ground terminal of all devices in your circuit together. This provides the necessary common ground reference voltage for them to interoperate. Your voltage divider needs to go from 5 vdc to 3.3 vdc. There are two considerations in setting up a voltage divider: a. it provides the proper voltage, and b. ...


3

I do not think there is any Pi circuitry to return the current supply voltage. As far as I am aware the under voltage circuitry is a piece of hardware which triggers at 4.65V. So you could discriminate between two values, more than 4.65V or less than 4.65V. The only justification for this answer is I remember dozens of posts where people have asked the ...


3

Question Let me first summarize the OP's question. He has a 220VAC water pump. He knows that a 555 IC can tell AC current on by blinking a LED. His question is how to let Rpi talk to 555 to find the pump is on or off. Research I am guessing how 555 detects AC current. As soon as the AC current passes a wire, electromagnetic field is created. ...


3

Not entirely. There are two Q&A you should read: 1, 2. The first Answer tells us that the voltage output from the USB supply is regulated iaw the USB standards, and therefore needs no further regulation on the RPi. So, I'd say the answer to your question is, "the 5V pads are regulated iaw the USB specifications and standards". The second Answer is ...


3

The Pi has 3 "components" the CPU, GPIO and Video Core which are relatively independent. Even when the Pi is shutdown the Video Core continues to run, and the GPIO pins retail their state; only the CPU is not running. The 3.3V is supplied by separate circuitry and will be present while ever the Pi is connected to a 5V supply. The best way to reliably ...


2

You will still be exceeding the maximum voltage of the GPIO (admittedly not by much). There is no allowance for tolerances; ±5% for resistors, ±2.5% for external power. Good design always makes allowance for worst case values. There is also NO NEED; GPIO will be low if <0.8V; high if >2.2V so I suggest you design for 2.3V The ACTUAL threshold for GPIO ...


2

I believe the Pi will be fine with that arrangement. The voltage (3.4V) is slightly larger than the official 3.3V limit. The excess current will be easily handled by the GPIO protection circuitry (excess voltage 0.1V, resistance 4700 ohms, current 21 microamps). Remember the resistance values may be +/- 20% anyhow.


2

The Pi's GPIO are to set logic levels (on or off). They are not designed to be a voltage reference. The 3V3 rail is regulated. You'd have to see the specs for your Pi model to find the actual regulator used. I doubt if it is calibrated or particularly stable.


2

I assume that the LED is a 100mA type? And from the PN2222 data sheet we assume the gain of the transistor is 100 or so. This means the transistor current will need to be arround 1mA, and the GPIO voltage is 3.3v. Using Ohms law, 3.3/0.001 = 3k3, or if you take into account the bias voltage, (3.3-0.6)/0.001 2700 ohms, and this would be my choice. To recap.. ...


2

The default state of pins is given in http://www.panu.it/raspberry/ The default Device Tree settings configure most pins as inputs, some with pullup others with pulldown. Pins set as input cannot be said to "have a voltage", except for the high value pullup resistors they are in a high impedance state. Any voltage you measure is a artefact, and depends as ...


2

There is no such thing as "12V current" or "5V current" and you can NOT control a relay from a Pi (or an Arduino for that matter), neither can you "transform 5V current into 12V current". You can use a relay to switch 5V, 12V or even mains voltages. There are large numbers of relay modules, which consist of a relay and some electronics to switch this from ...


2

It may work, if I had to guess I'd say it would work. There should be no problem powering the relay from a Pi 5V pin (and a Pi ground pin). It will be quite safe to connect a Pi GPIO to the relay signal pin. The only question is whether a Pi GPIO high (3V3) will be enough to be seen as high by the relay logic. A lot of devices see the minimum high as 70% ...


2

Everything looks fine. Yes, you need to connect the Pi ground to the ground of any sensors you connect to the GPIO. It doesn't matter if they are powered by the Pi or by an external power source. You need a common voltage reference so both ends know what's high and what's low. The resistor divider is fine. There are many examples on-line. This is ...


2

As noted in Raspberry Pi Power Limitations (which you referenced) The newer Pi(3/2/B+) have a voltage monitor chip (APX803) which triggers at 4.63±0.07V. The Pi3B+ Pi3A+ use a MxL7704 chip to manage power, which has the same nominal trigger point. The Pi has NO voltage measurement circuitry, this is an on/off trigger and there is no analog measurement ...


2

You need to do a power budget. I would recommend a external power supply for 5volt devices. You also need to interface the PIR's 5volt output to Raspberry Pi's GPIO of max 3,3volt. Either you can do a voltage divider or modify the PIR to 3,3volt. simulate this circuit – Schematic created using CircuitLab https://www.instructables.com/id/Convert-a-...


2

Update 2019apr08hkt1109 On second thought, the question can be laser cut to focus on a very specific topic: "How to measure the magnitude of AC current in the range of 0 ~100mA, with a generous tolerance of 20%?" I think we can begin our feasibility study with two current sensors: (1) AC712, (2) INA12x/22x, ... ACS712 (or newer ACS723) 5A full scale ...


Only top voted, non community-wiki answers of a minimum length are eligible