13 votes

How can I calculate a relay's series resistor?

I have been told that always that I add a relay to my design I have to include a series resistor (series with the coil) to limit current in it. This is wrong advice. The relay's datasheet will tell ...
Transistor's user avatar
  • 171k
12 votes

Would a solderless breadboard be able to handle 20V without short circuiting?

I've put 2000V on breadboards before, though with careful monitoring, current limiting, and avoiding nearby positions. Possible they might even handle as much between adjacent positions... at least ...
Tim Williams's user avatar
8 votes

How can I make a more permanent connection to cheap sensors?

Looks like they're 2.54mm pitch and flat, so you could use a SIP or DIP socket such as an 8-pin socket like you'd use for an 8-pin DIP IC. Not the machined type, which probably won't fit well, the ...
Spehro Pefhany's user avatar
8 votes

Would a solderless breadboard be able to handle 20V without short circuiting?

The safe limits will depend upon the quality of the solderless breadboard. As an example, Multicomp specifies the voltage and current limits of their solderless breadboards as 300 V and 3 A. A safe ...
user354153's user avatar
6 votes

How can I make a more permanent connection to cheap sensors?

If the supplied leads are too short, you could solder extra wire to them, heat shrink the splices, and then use the longer lead length to connect to any type of connector you like.
vir's user avatar
  • 16.2k
6 votes

How can I calculate a relay's series resistor?

If you have a 5V relay, you give it 5V without series resistors. I guess what you have been told applies to a case where you have e.g. 12V supply and relay with 5V coil, then you need to have ...
Justme's user avatar
  • 137k
4 votes
Accepted

What is the purpose of the Zener diode in this voltage smoothing circuit?

This circuit is not generally looked at as a low pass filter but as a regulator with bypassing. The Zener and resistor are used as a shunt voltage regulator. The capacitor is to bypass the regulated ...
GodJihyo's user avatar
  • 19.6k
4 votes

Would a solderless breadboard be able to handle 20V without short circuiting?

Generally, yes. Should be no problem. The weakest insulation on most breadboards is on the back, between the breadboard and whatever it's mounted on (if anything). This is often just a thin paper or ...
Dave Tweed's user avatar
  • 170k
4 votes

Simplest voltage-controlled constant current source outputting 500 mA

The error in your simulation is that R2 is 0.5 ohms and V2 is 1 volt. 1/0.5 = 2A, not 0.5. Change V2 to be 0.5V and R2 to be 1 ohm. The reason that the circuit isn't reaching 2As is that 9V/(0.5+10+0....
OM222O's user avatar
  • 347
4 votes
Accepted

How to design an I/V Converter for Arduino

For a simple setup, i would use this approach: NOTE: I don't fully understand why you want a 0-4.5V signal range? simulate this circuit – Schematic created using CircuitLab NOTE: This circuit ...
ElectronicsStudent's user avatar
3 votes

Would a solderless breadboard be able to handle 20V without short circuiting?

20 V is fine. Too much current can be an issue. The contact resistance is huge and can be 1 ohm. This means that the practical current limit is about 100 mA. I highly recommend a lab power supply ...
Mattman944's user avatar
3 votes

What is the purpose of the Zener diode in this voltage smoothing circuit?

As far a depictions go, I'd draw the circuit as follows: simulate this circuit – Schematic created using CircuitLab This makes it perhaps more obvious that R1 is dropping down voltage, and that ...
Kuba hasn't forgotten Monica's user avatar
3 votes

Pros and cons to round PCB design

I would like to add to this question from our perspective as a PCB assembly company. So this is regarding the actual manufacturing of your product. To assemble the bare PCB, all PCBA companies will ...
Newmatik's user avatar
3 votes
Accepted

RPi - Water pump control using MOSFET

You should consider using this modified circuit: - Regarding the MOSFET (rated at just over 1 amps continuous), it's unclear what current the pump takes despite reading the data sheet. I suspect that ...
Andy aka's user avatar
  • 443k
3 votes
Accepted

What does mean NC in an schematic and BOM?

BOM — bill of materials — shopping list NC — no connection / do not connect NC is used the wrong way in this BOM. It should say “spare” instead.
Janka's user avatar
  • 14k
3 votes

How to design an I/V Converter for Arduino

To convert current to voltage, we need to take a look at ohms law: V = I*R more specifically, I = V/R. If you take your varying ...
Pxl's user avatar
  • 326
3 votes

How can I calculate a relay's series resistor?

The value of 140 mW is not its rated power; it is just its nominal power dissipated at the nominal voltage. It is completely fine to operate the coil directly from 5 V DC, as long as 5 V DC is within ...
Leonardo Márquez's user avatar
3 votes

How can I calculate a relay's series resistor?

There definitely is a reason to limit the holding current of the relay, especially if you care about the power consumption. For that case one may use parallel RC circuit in series with the coil. The ...
Trumpf's user avatar
  • 31
2 votes
Accepted

LDO LM317HV Problem With Output Voltage

The regulator needs enough current throught it for maintaining proper operation as a regulator, and you have no load. TI LM317HV may required up to 12mA through it to work, typically 3.5mA. Your 1.37k ...
Justme's user avatar
  • 137k
2 votes

Dual N/P-Channel MOSFET Dies with Smoke

When Q1 turns off, the drive is limited by the 47K resistor. The charge time is about R2 x total gate capacitance, or 47K x 3nf = 141us, and during this slow transition the n and p transistors burn as ...
Daryl Diamond's user avatar
2 votes

How can I make a more permanent connection to cheap sensors?

My brief googling of the subject suggests you want to look into Clincher(tm) flex connectors from Amphenol.
vicatcu's user avatar
  • 22.6k
2 votes

How to choose/connect the appropriate MOSFET-driver for a power MOSFET? Driver breaks down

The physical layout of the entire system is very important. You’re switching high enough currents, fast enough to make parasitic inductances act like automotive ignition coils. If you post the layout ...
Kuba hasn't forgotten Monica's user avatar
2 votes

I had a custom Arduino Board fabricated, and I can't load it with a bootloader

You need firmware for both AVRs. Mega16U2 needs firmware to work as USB serial UART interface if you want to communicate between PC USB and the Mega328. It will not even show up as an USB device ...
Justme's user avatar
  • 137k
2 votes
Accepted

How can I detect black and white using an LED and a photodiode with an STM32?

You may be able to use a comparator, or if your MCU has analog inputs, connect Q1 directly to the MCU. But, the first step is to characterize your sensor. Build the left half and run some tests. See ...
Mattman944's user avatar
2 votes

TDA2822D speaker connection issue

The schematic has been edited to clarify your doubt.
vu2nan's user avatar
  • 17.5k
2 votes

Solving for values in an NPN bipolar transistor circuit

It would help to know what simplified model of the circuit was used in finding those values. It turns out that the transistor was modeled as a current-controlled current source, with a fixed base-...
Kuba hasn't forgotten Monica's user avatar
2 votes

I want to control the voltage and current of a LTC3780 module using an Arduino

There are a ton of Chinese modules that say they use the LTC3780. Without more information (specifically, a good schematic) it's hard to say exactly what could go wrong. The pricing suggests the ...
Spehro Pefhany's user avatar
2 votes
Accepted

Problems with choosing resistors for a common emitter - voltage divider bias amplifier circuit

There's nothing wrong with your calculations and approach. The issue is with the design because of a relatively low voltage gain without any emitter degeneration. If we were talking about higher (e.g. ...
Rohat Kılıç's user avatar
2 votes

Problems with choosing resistors for a common emitter - voltage divider bias amplifier circuit

You can pretty much determine collector current from the power requirement and the supply voltage. So, 0.2 watts divided by 15 volts = 13.333 mA so, broadly assume the collector current is 10 mA. That ...
Andy aka's user avatar
  • 443k
2 votes

How can I calculate a relay's series resistor?

Very good question... It takes me way back to my 70s school days when I was making all sorts of devices with relays. Then I reasoned like the OP does now: The relay coil was wound with copper wire, ...
Circuit fantasist's user avatar

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