Tagged Questions

2
votes
0answers
57 views

Turning OFF the grill when the espresso maker is ON

These are the variables to this problem: We have two 120 volt appliances: - an espresso machine (draws 8 amps) - and a grill (draws 12 amps). The grill is ON all the time (it actually stops heating ...
2
votes
2answers
129 views

Is this a 5V to 3.3V level converter?

Need to repair a legacy system that has been discontinued and am confused by the PNP based circuit below. The input signal (max. freq = 20Khz) is applied at IN and is active low. It's TTL level. It ...
4
votes
1answer
172 views

how to design a switch which works when an input of 0.10 is applied

i have an alarm clock , it's output voltage to the alarm buzzer is around 0.15 volt , i need to attach an electrical appliance to make it operate on scheduled time , for that i had used this circuit ...
3
votes
1answer
84 views

Connecting a N.O. grounded switch to a scanning switch matrix

I am working on a project that includes a scanning switch matrix. It also includes a joystick with an integrated push button. I am out of IO pins on the micro, but there are gaps in my switch matrix, ...
5
votes
2answers
457 views

Switching a current with an NPN transistor and a P-MOSFET

Just learning about transistors and I'm trying to clearly understand how to apply them for basic switching, in terms of the two standard cases, i.e., Active HIGH behavior and Active LOW behavior. For ...
4
votes
1answer
258 views

Selecting proper vales of Rb, Re and and Rbe in a NPN transistor emitter follower configuration?

I need to gate a TTL Tx pin @115000bps as the chipset that drives the RxTx lines do not implement UART BREAK for arbitrary time periods. As a quick hack I have come up with the following ...
1
vote
2answers
343 views

5-pole, double-throw relay

I am working on an electronics project where I need a two way switch, that can be controlled using an arduino and can be soldered by hand. I tried to Google for it, but without luck. Does anyone know ...
2
votes
3answers
467 views

Transistor question and is my circuit safe for Raspberry-Pi?

This is my first circuit designed from scratch (that actually does something interesting), so please be patient with the beginner's mistakes (and maybe point them to me). My circuit is the following: ...
0
votes
1answer
141 views

Drive relay when “key” is connected

I'm trying to design a circuit that will drive a relay (and thus turn on a bigger circuit) when the correct "key" circuit is connected. The "key" is contained within the hashed box and functions as I ...
1
vote
1answer
225 views

Alternative to optocoupler? Other switching devices?

I have a part that classifies what kind of power I get on ethernet by presenting different loads. For example, the part needs to have a 100 Ohm resistor across two of its pins, and the part will ...
0
votes
2answers
353 views

Emulate many-pole, dual throw switch with transistors

How can I use transistors and other discrete components to make a circuit that functions like a DPDT (double pole double throw) switch, and can be extended for any number of poles required? For ...
4
votes
2answers
2k views

P-Channel MOSFET high side switch

I am trying to reduce the power dissipation of a P-Channel MOSFET high side switch. So my question is: is there any way in which this circuit can be modified so that the P-Channel MOSFET will ...
2
votes
2answers
1k views

Driving a large 7 segment display using a micro-controller

I need to drive a large seven segment display (segment length is a about 2 inches) using a micro-controller (PIC 16F877). I've driven normal seven segments directly from PICs without issues, but I ...
4
votes
4answers
374 views

Replacing a switch with a transistor

I am working on a project on the Raspberry Pi, it is a bit experimental as I am learning the electronics side as I go along... please edit out any problems with terminology. My aim is to replace a ...
6
votes
1answer
214 views

What's the difference between small signal bipolar junction transistors (BJTs) marketed as switches vs. amplifiers?

For instance, the MMBT3904 and MMBT3906 BJTs are listed as NPN/PNP Switching Transistors, and the datasheets mention the switching times, while the BC846 and BC856 BJTs are listed as NPN/PNP general ...
20
votes
2answers
477 views

What's the difference between field-effect transistors (FETs) marketed as switches vs. amplifiers?

For instance, the J108 JFET is listed as "N-Channel Switch", and the datasheet mentions the RDS on resistance, while the J201 JFET is listed as "N-Channel General Purpose Amplifier" (and the ...
4
votes
1answer
320 views

How can I use a transistor as a switch?

I'm trying to drive a DC motor using an external voltage source and control it using a transistor switch. It doesn't seem to be working during the simulation though. I know I must be doing something ...
1
vote
1answer
465 views

Silicon Controlled Switches: applications&suppliers

I came across this description of what are called "silicon controlled switches." I always look to balance n/p-channel electronics for stability, and using these silicon controlled switches seemed like ...
8
votes
4answers
2k views

What is wrong here? - A simple NPN switch

I have a simple npn switch, see the diagram. I feed a 100KHz square wave (TTL) to the base of this transistor and it turns on very very fast (a few nSec) but it doesn't turn off as fast, it almost ...
26
votes
5answers
2k views

Why do you need 2 resistors when hooking up a transistor as a switch

What is the point of R2 in the following diagram: I get that R1 controls the current to the Base, but what does R2 do? Thanks!
1
vote
2answers
334 views

Not use current limiting resistor for switching device on off using TIP122 possible?

I wanting to control MP3 player and amplifier box through PIC board. My project is doing announcement when person standing in near PIC board with proximity sensor. When proximity sensor detecting ...
1
vote
1answer
373 views

What kind of resistors do I need to use in this Canon remote switch, if it is possible at all with the P2N2222A transistor I have?

I'm a total electronics n00b set out to create an intervalometer for my Canon EOS 350D camera which seemed super simple from the outset, but I got a bit blocked with creating a switch using a ...
5
votes
4answers
718 views

How do transistors replace the electromechanical switch in an inverter circuit?

Quoting from wikipedia: "In one simple inverter circuit, DC power is connected to a transformer through the centre tap of the primary winding. A switch is rapidly switched back and forth to allow ...
10
votes
2answers
920 views

How to choose a switch?

There seem to be about 4 major flavors of transistors, and then there are NPN/PNP versions. There are also relays, SCRs, and TRIACs. When I need an microcontroller-controlled switch, what rules of ...
5
votes
4answers
451 views

Vacuum tube systems in apollo era space missions

I hope this is the right place to ask this. But my friend is just learning about electronics and just was given an old vacuum tube. Just because I'm curious, is there any technical information on the ...
8
votes
3answers
1k views

Need help operating a transistor

I have a relay operated by an NPN transistor that needs some voltage applied to the base. I'm working with an arduino and if I give it a digital port, all's well. The circuit looks like this one: ...