Voltage Follower Also called a buffer. Only the OpAmp tiny bias current is drawn from the signal source. Voltage follower with output diode drop removal Non Inverting Amplifier Vout = Vin x (1 + (R2/R1)) E.g. R1=10k, R2=10K, Vin=1V, Vout=2V Only the OpAmp tiny bias current is drawn from the signal source. Inverting Amplifier The […]
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OpAmps General
The Basics No current flows in or out of the inputs. (Well actually a small bias current does, but its small) Output goes positive if the + input is more positive than the – input. Output goes negative if the + input is more negative than the – input. Output will do whatever is necessary […]
Microphone Pre Amplifier
A good microphone pre amp circuit we've used in product designs:
Reverse Polarity Protection
This trick using a P channel mosfet is a common way to provide reverse polarity protection on a power supply input. It avoids the voltage drop problem of using a diode, with just the resistance of the mosfet to consider. Important – ensure you don't violate the mosfet max Vgs and Vds specification! Here's an example […]
Interfacing different signal voltages
3V Devices to 5V CMOS 4 connections: 74HCT125 is a good cheap choice (14 pin package, quad 3-state buffer).Power at 5V. Connect each of the 4 output enable pins to 0V. The min high input voltage is 2V so 3V3 compatible and the output state matches input state (it’s a straight buffer). 74HCT08 (quad AND […]
Universal Mains Input Detect
The circuit below provides a simple method to detect a mains voltage input with an input range of 90 – 240V AC: The output gives a low signal for around 90% of the time when a mains input is present, so you need to connect it to an edge detect input of a microcontroller (e.g. […]
PCB Short Finder
Finding shorts in PCB's can be a nightmare. Digital multimeters typically don't measure down to the <1mOhm level required to trace down where the fault is located. This "Model 1000 Short Finder" seems a bit basic and costly for what it is, but it's another worth it's weight in gold tool when it's needed. Update […]
Beta Reflow Kit
We we're sceptical when we purchased this but it's turned out to be a great buy. Previously we assembled most prototypes in house using a compressor and precision liquid dispenser to place a blob of solder on each pad, then placing the SMD component on and then soldering each pad with a soldering iron. The […]
Programming Using The Microchip PICStart Programmer
This guide is old! We no longer design products that require the PICStart Plus programmer. The Microchip PICStart Plus is a simple low cost programmer for DIP IC's. Ensure your PC is running the latest version of MPLAB IDE (not MPLAB X, may be downloaded from www.microchip.com). Connect the PICStart Plus programmer to your PC using […]
Alkaline Batteries
The typical voltage range for an alkaline battery is 1.55V to 0.8V as it discharges.