PC SOUND-CARD SCOPE INTERFACE FACILITATES DC RESTORATION Waveform before correction The 555 Timer IC when operated as an astable oscillator from 5V provides a square wave of 0-5V and the waveform at the timing capacitor varies from 1/3 to 2/3 of 5V. The first screen shot shows the timer IC 555 AC coupled waveforms as captured by the PC sound-card. It can be seen that the zero settles at the average value. (The input has been scaled by 1:10 to remain within the input voltage limits.) The square wave shows a peak value of 171mV instead of 5V and the capacitor waveform appears to be centered at 0V with a peak value of 66.59mV. The interface circuit provides two peak-hold circuits which provide the positive and negative peak DC value of the input waveforms. We can compute that the square wave needs to be offset by 468mV -171mV = 297mV and the capacitor waveform by 283mV - 66mV = 217mV. Waveform after DC restoration The second figure shows the waveforms after entering the offset values 297mV and 217mV into the offset boxes for CH1 and Ch2.
Reflow Skillet Skill Level: Beginner by Nate | July 01, 2006 | 47 comments I've been reflowing SMD parts on PCBs for around a year now. Don't get me wrong, there is the correct way to manufacture 10,000 units of a caller-ID controller board, and then there is the Spark Fun way. Here is a tutorial that will break down the different approaches to SMD reflow soldering, what we've learned, and what to steer clear of. As always, this stuff can kill you, burn your house down, or make your basement smell pretty foul. SMD Reflow Tutorials: There are five ways to solder SMD parts that I can think of: Hand Soldering - Hand soldering is cheap (no extra equipment needed). New users to soldering SMD devices are always intimidated by soldering itty-bitty leads. Common questions: Do I need a microscope? Maybe. Do I need a super fine tip? Probably not. I certainly can't hand solder XY type package! No really, you can! Over all, hand soldering is the way to do it when other means are not available. Pros: Cons: Toasting -
Charlieplexing Charlieplexing is a technique proposed in early 1995 by Charlie Allen at Maxim Integrated for driving a multiplexed display in which relatively few I/O pins on a microcontroller are used to drive an array of LEDs. The method uses the tri-state logic capabilities of microcontrollers in order to gain efficiency over traditional multiplexing. Although it is more efficient in its use of I/O, there are issues that cause it to be more complicated to design and render it impractical for larger displays. These issues include duty cycle, current requirements and the forward voltages of the LEDs. A Charlieplexed digital clock which controls 90 LEDs with 10 pins of a PIC16C54 microcontroller. Traditional multiplexing Display multiplexing is very different from multiplexing used in data transmission, although it has the same basic principles. Charlieplexing When using charlieplexing, n drive pins can drive n digits with n-1 segments. pins. Complementary drive Refresh rate
Arduino UNO Tutorial 6 - Rotary Encoder Arduino UNO Tutorial 6 - Rotary Encoder We have written a tutorial for Rotary Encoders using a Microchip microcontroller but now would be a good time to make an Arduino UNO version. With a rotary encoder we have two square wave outputs (A and B) which are 90 degrees out of phase with each other. The number of pulses or steps generated per complete turn varies. The Sparkfun Rotary Encoder has 12 steps but others may have more or less. The diagram below shows how the phases A and B relate to each other when the encoder is turned clockwise or counter clockwise. Every time the A signal pulse goes from positive to zero, we read the value of the B pulse. We will now use the rotary encoder in the simplest of applications, we will use it to control the brightness of an led by altering a pwm signal. We will use the sparkfun encoder as discussed above. Each time our timer code triggers, we compare the value of our A pulse with its previous value. The schematic is shown below
microcontroller - Arduino/Atmega with TIP120/121/122 transistors: base current question High-Power Control: Arduino + N-Channel MOSFET Eventually you are going to find yourself holding a 12v solenoid, motor, or light and wondering “How the heck am I supposed to control this from my Arduino?” And we have covered this in the past. Today we are going to talk about another way of doing just that, this time with an N-Channel MOSFET metal–oxide–semiconductor field-effect transistor, specifically the RFP30N06LE MOSFET (You can pick these up from sparkfun). but you can use any N-Channel MOSFET exactly the same way. How this works WARNING: I am about to simplify the crud out of this, so beware… it is here in an attempt to explain, in simple terms, what is going on. First off, a MOSFET is a transistor, just a special kind. If you don’t know transistors at all, they are 3 lead components that have 2 simple functions, to switch or amplify (in this example it is setup as a switch). So we connect it so that our motor, solenoid or light is connected to V+ but not ground (V-). More Information Hooking it up / What’s the diode used for?
driver - How can I efficiently drive an LED? A current source based on a JFET In Lecture 1 we introduced the idea of a current source, and mentioned that these were slightly more difficult to implement than the perhaps more familiar voltage source. We are now in a position to learn a practical way of implementing current sources. The circuit schematic below (which has been entered into the pSpice circuit simulator) shows a simple way of doing this using a JFET (see Lecture Notes page 86). Note that the symbol used for the JFET, type 2N3819, is not quite the same as the more widely accepted one we have encountered! The negative terminal of the supply V1 (battery symbol) is connected to Ground, also known as Node 0, and represents the reference point for any measurements we might make. The circuit can be described as a self-biased JFET: the source resistor R determines the gate source voltage through the relationship VGS = -VS0 = -ID R Using pSpice to predict the behaviour of the circuit The family of curves shown above represent the pSpice output.
FET Constant current drivers for LED display using BF256 FET Constant current drivers for LED display using BF256 This is a FET Constant current drivers circuit for drive LED display which can use FET-BF256 instead resistor so well. Normally when you use LED display in any circuits often use a resistor for limit LED current. But it is not best, this way is ideal for the stable voltage source only. Such as in digital logic probe circuit, which we need to test to TTL type that use 5-volts only, and a CMOS type that wide voltage of 3-volts to 16-volts. I have a good way. I use number : BF256 normally it is used as N-channel RF amplifier (in VHF/UHF frequency) , it is small size FET to-92 type. And I test it on a breadboard as video below. Firstly I adjust voltage at 5V (see on meter above) At the same time, I measure current that flow through LED have 4.22mA only. Then, I adjust voltage up, while the current is stable about 5mA only and the LED also stable brightness as we need…happy circuits.