transistors - Why is there a delay in a common anode 7-segment display?

I have a common anode 4-digit 7-segment display. I have each segment cathode connected to a 330-ohm resistor, and the resistor is connected to a shift register. Each segment cathode is connected to the same shift register. Each common anode is connected to a second shift register. Right now, I am using an Arduino to multiplex the display to show a number.This works great, but there's a problem. The display isn't bright enough! I assume because this is a common anode configuration, and that the shift register can only provide about 40mA of...Read more

transistors - Can reverse voltage gain for a BJT be negative?

While observing the input characteristics of a Bipolar Junction Transistor(BC547), I observed from the graph that the reverse voltage gain came out to be negative. Is this possible and if so, what is it's physical significance? If not, is this observation simply due to the non-ideality of conditions of the experiment or just some error?simulate this circuit – Schematic created using CircuitLabNote that both sources shown in schematic are not actually just 30V, they can be varied from 0 upto 30 V.Updated the schematic. Note that I am plott...Read more

switches - Controlling a Solenoid With Raspbery Pi GPIO Output Using a Transistor

I'm trying to control a solenoid using the RasPi 2's GPIO pins. Since the solenoid needs more power than the RasPi can provide, I'm using a 9V battery to provide the power.I started with just wiring the circuit and checking if it works by connecting and disconnecting the 3v3 output to the board.First, here's the wiring I'm currently using:The diode accross the solenoid inputs is a standard flyback diode, and the resistor is a 1kOhm resistor.Apparently the RasPi GPIO output pins produce 3.3V at a maximum draw of 16mA.The inductor represents my s...Read more

rf - Transistors' Scattering Parameters

I have some doubts about the Scattering Matrix of a transistor seen as a 3 port devices. Precisely, I read (for instance here) that we do not have 9 independent S parameters since there is this relation (6 equations):So there are only 4 independent S parameters, and this is correct because generally transistors are described as 2 port networks. But I do not understand the proof of these relations. It is shown in these pictures:First question: is the fact that the sum of current = 0 always verified? Is it a sort of Kirchoff Current Law?Second qu...Read more

transistors - Motor "load" for 8051 does not change based on 8051 GPIO pin

I implemented a circuit very similar to the following (original source: 8051 - Can an NPN transistor be driven?) to control power to a vibration motor from my micro.I made the following modifications:Power supply is 5V DC regulated, not 3.3VR1 is changed to 100K (to try to save battery power)R2 is changed to 1K (to pass GPIO pin value to transistor easier)Q2 is TIP31PowerV is not a separate supply. Instead it is replaced with a 51 ohm 1/2 watt resistor connected to the same 5V DC regulated supply to prevent the rest of the circuitry from overhe...Read more

transistors - Why does this amplifier not work past a given Vcc?

This circuit works well enough in simulation, I've built it and I can't get the final stage to put more than around 16V across the load.The last stage itself is performing like a voltage follower in that the voltage to this stage seems to cap off at around 17V, however when common emitter stages are in isolation they turn on and (almost) 28V can be switched.Dropping the final stage's base resistor values actually worsens the problem - i'm stumpedThe 300R simulates the AC equivalent load i'm working with, which is a piezo pump...Read more

transistors - How to turn on LED using RF as a catalyst?

I am trying to build a circuit that turns on a LED diode when it detects AM radio waves, in order to create a "radio wave detector". Before I explain further, please note that I am not trying to power the LED solely using RF power from the air. In fact, this wouldn't be possible because I read that radio waves that we pick up are typically around 50-100 μV. Thus, it wouldn't be possible to power the LED using just this power.Instead, what I want to do is amplify the relatively faint AM radio signal using extremely basic components like a trans...Read more

transistors - Inverted high impedance / pull down circuit

I'm devising a circuit to control the shutdown input on an integrated circuit. The IC accepts a high impedance input (can't be pulled to any voltage) to enable operation, or it can be pulled down to disable operation.I'm trying to control it with a logic signal which is either 0V or 3.3V. This would be relatively simple with a low-side NPN/N-fet. However I want it to operate in an inverted way, where a 0V input will result in the output being pulled down and 3V3 input will give a high impedance output.What kind of circuit could I use for this? ...Read more

transistors - Indicator light circuit

I'm an electrician and my work is to maintain boats.I have a problem. On the boats are sailing lights, and for each sailing light is another light inside the boat that tells you if the sailing light is working or not.This was no problem with the old 40W incandescent light bulb but now all the lights are LED and the trick doesn't work any more.This is the sailing light I'm using:Hella marine. NAVILED PRO TOP. 2LT 959 908-5. Operating Voltage 9 to 33V DCPower Consumption Less than 2W (0.14A@12V / 0.08A@24V)So this is what a have on the drawing o...Read more

transistors - Sending flyback current to another inductor using crossed diodes

So, here is the context. We have two electromagnets (modeled as R1 and L1, and R2 and L2), their state is dictated by a microcontroller which sends PWM to Q1 and Q2. The signal sent to Q1 and Q2 is a square wave around 80 Hz. The two square waves have the same period and amplitude, but an 180 deg. phase shift, so when Q1 is open, Q2 is closed.Here is the idea: when the switch to an inductor is suddenly opened, a flyback potential is created across the inductor. A diode pointing to the other side of the inductor is usually added to avoid arcing....Read more

transistors - Phototransistor as a pull-down in digital circuit

I have very little experience with phototransistors. I'm trying to create a circuit that will effectively function as collision detection. I'm using OPB608A which utilizes an NPN transistor. My goal is to use said transistor to output logical signal to my PIC18F4520. The I/O pin I'm using for this has Schmitt Trigger Buffer - according to the datasheet any input above 0.8VDD (~4V) will be treated as logical high (and 0.2VDD - 1V - will bring it back down). Having very little experience I am tempted to use the following circuit: and adjust value...Read more

transistors - Easiest way to connect two pins when an output is off?

I'm planning to build a switch that turns off the power supply to my Raspberry Pi when an integrated circuit (ATtiny 85) output pin is low. The power supply (Adafruit PowerBoost 1000C) goes off when the EN pin is connected directly to the ground. I've been trying to use an NPN transistor inverter circuit to do this, but I haven't had much luck. I can use the transistor (without inverter) to turn the power off when its base goes high (connecting the EN to collector and ground to emitter), and I can use the transistor inverter to turn on/off an L...Read more

transistors - Easy High Side Driver

Had a few issues with a high side using darlingtons etc - what would be simplist 3v3 logic driven hi side (12V output) driver (I'm thinming fet) that can handle 1-2A for running a solenoid, as a switch - frquncy is VERy low like on for 10 mins, off for 5 etc.tia...Read more

pulldown - Using a transistor to control a pull-down switch

simulate this circuit – Schematic created using CircuitLabI have a Runcam 2 video camera. It uses a temporary switch to turn on/off and start/stop recording. I would like to control these functions with an arduino. Once side of the switch is 3V the other is ground. Pushing the switch pulls the 3V to ground. I've soldered two wires to the switch and can operate the camera by shorting the two wires. I would like to use an NPN transistor with the base controlled by an arduino pin or other suitable method to operate the camera. I've se...Read more