Power supply for Raspberry Pi

Before you tell me that the question has already been asked, only similar things have been asked. I need to power a Raspberry Pi with some electrical equipment attached to it. The Pi needs to run for at least 48 hours and I need at least 2V and 900mAh to be used for the other…

Creating a logic function of a burglar alarm system for a bank

This is the problem from homework that I am stuck on: A burglar alarm system for a bank is to be operative only if a master switch at the police station has been turned on. Subject to this condition, the alarm will ring if the vault door is disturbed in any way, or if the…

How can I measure the pressure from my strain gauge?

I bought a strain gauge from RS components, and I want to find out how can I get the pressure from the measured voltage on the strain gauge. I managed to the Wheatstone bridge and supply it with a voltage as Vex. Based on this document, the manufacturer will provide the conversion formula but on…

Measuring current with multimeter (broken?)

I just got my first multimeter from Home Depot and it was $60. It’s the Extech EX330 and it works fine except for when I measure current. I am doing it correctly and the fuse has not been blown. When I put it on the amp setting it reads .06 A when I put it…

ATtiny2313 vs ATtiny84 software compatibility

I make and sell a variant of the USBtiny AVR programmer. It uses an ATtiny2313 clocked at 12 MHz and does bit-banged USB using hand-tuned assembly language (that someone else wrote – it’s an open hardware / open firmware project). In an attempt to reduce costs, I’d like to shift from using the 2313 to…

Using transistor as switch with low voltage

Basically, I need to monitor a circuit’s output so I can activate another system. The output voltage of active stage is 140mV. If I am not wrong (from what I read about transistors) 140mV is not enough to put a BJT transistor into saturation (ON mode). The end goal is turning on an LED and/or…

Calculate the average power dissipation in Joules

I’m self-studying this problem, and it seems that have a problem solving this. The only thing I didn’t understand is this solution is how to calculate the average power dissipation. It’s never mentioned in class and I can’t find any formula even to proceed. I know that: pavg=Vm⋅Im2p_{avg} = \dfrac{V_m \cdot I_m}{2} And I don’t…

Finding Equivalent Thevenin Resistence

For the following circuit: I’m solving for the Rth at node 2. In the solution guide, it shows that the Rth = (10k || 10k). I don’t understand how this is so, by following the resistence equivalent rules, these two resistance should be in series. I’d appreciation for the clarification. ================= ================= 1 Answer 1…

Unregulated AC-DC adaptor voltage response

This is my first post. I’m a long-time computer programmer but new to this field of hobby electronics. I bought a 12V 800mA AC/DC adapter to feed my circuits. Seems it’s unregulated since the multimeter reads ~18V at 12V without load. Reading some information online, I discovered this behavior is due the regulated / unregulated…

Is there any way to interface 4×4 matrix keypad using 2 IO lines

I have two IO lines and wants to interface 4×4 matrix keypad. Using MUX ICs I need 4 IO lines. Is there any method to achieve it using 2 IOs? ================= ================= 3 Answers 3 ================= I have done it by using an I2C GPIO expander chip. I used the Microchip MCP23017, but there are…