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 ...
- 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 ...
- 27k
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 ...
- 384k
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 ...
- 81
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.
- 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 ...
- 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 ...
- 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 ...
- 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....
- 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 ...
- 3,081
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 ...
- 15k
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 ...
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 ...
- 91
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 ...
- 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.
- 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 ...
- 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 ...
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 ...
- 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 ...
- 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 ...
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.
- 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 ...
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 ...
- 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 ...
- 15k
2
votes
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-...
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 ...
- 384k
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. ...
- 30.2k
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 ...
- 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, ...
Only top scored, non community-wiki answers of a minimum length are eligible