Schmitt trigger is a special logical element adjusted to work with analog input signals. The primary purpose of Schmitt triggers was to restore the shape of digital signals. Because of the transmission line effect, digital shape transforms from square to trapezoid or triangle or more complex signal. Of course, during transmission, signals become noisy and distorted. Schmitt trigger is a comparator circuit, but positive feedback results in hysteresis and memory effect. Comparing to simple logical elements, Schmitt triggers have two threshold levels. Between these threshold values U1 and U2, the state of output doesn’t change the so-called hysteresis. Such an effect stabilizes output against rapid triggering by noise. Bellow is two characteristics compared of simple logical inverter and Schmitt trigger inverter:
There are currently huge amounts of different digital IC chips available in the market, starting from the simplest logical elements and ending with processors and gate arrays (FPGA). Of course, there also are lots of IC manufacturers offering IC’s. Many of them are specialized and won’t be reviewed here. Let’s limit ourselves to smaller, more general digital chips, basically TTL 74series. This series is produced by many manufacturers like Texas Instruments (TI).Common marking: Manufacturer identifier indicates the manufacturer name;
This is a fun project I found on Jon’s antique radios web-page. He has managed to convert the VGA output signal from PC to X Y X oscilloscope signal. Converting the VGA RGB signal to a synchronized oscilloscope input signal is pretty easy because VGA has two sync signals separate from RGB signals. Look at pin-out of VGA cable: Sync signals make things much easier as there is no need for additional sync signal generators – thus circuit becomes pretty simple without any programmable components:
This project was born for repairing broken PC monitors. This allows avoiding using a computer while testing monitor patterns. The Tiny monitor tester uses ATTiny2313 AVR MCU running at 20MHz speed. Such speed allows running synchro H and V signals directly from MCU ports. Also circuit converts R, G, B signals to analog using a simple R-2R resistor network. ATTiny2313 Monitor tester:
Sometimes you need a quick and easy solution for programming serial EEPROM memory chips. I think the easiest and well-known method is to use a simple programmer adapter with very few components: This adapter is connected to the RS232 port, and there is no need for an additional power supply as it comes from the PORT pin. The adapter is compatible with JDM Programmer so that you can use its programming software like IC-PROG. Just make a couple of settings, and you are ready to go:
I heard about this method and decided to try it with my board. I needed to replace the Atmega128 chip but didn’t have hot air solder for desoldering IC. I tried this weird desoldering technique, and I can say that I was satisfied. Tracks and other parts weren’t damaged. The Atmega128 board is working again as before.
I found an interesting article about the capacitance of ceramic capacitors may depend on voltage applied. In some designs, you can face a problem when ceramic capacitor capacitance may strongly depend on voltage. Few tests were done with various capacitors using the following circuit: In the circuit CX – tested capacitor; C0 – known capacitor. Voltage vas regulated from 0 to 50V using potentiometer R1. 50V is taken as the nominal voltage of the ceramic capacitor. Because Two capacitors are connected in series the total capacitance is C=CX·C0/(CX+C0) then we find the capacitance of tested capacitor CX=CÂ·C0/(C0-C); C0 is about 10 % of CX value. There were several capacitors tested and stunning results were found. – Some of the capacitors lost capacitance from 10 to 15 times due to the increase of voltage up to 50V. Even when 10% of voltage were applied the capacitance was only about 35 – 40% of nominal value. The only explanation may be that low-quality dielectric material is used in (no-name) ceramic capacitors. Of course, not all capacitors gave the following results. But be ready for this when using unknown producer ceramic capacitors.
Building AVR Jtag clone Finally, I found some time to finish the AVRJTAG clone. It was hanging for a while on a breadboard with a bunch of wires. I have made an Eagle CAD project with a PCB layout you will find at the article’s bottom. I didn’t change the circuit very much from the previous, just added ISP header(but didn’t have a chance to test it) and transferred to Eagle project as I didn’t find one ready to build:
A decibel is a special unit that is a little different from other measuring units in everyday practices. This is a nonphysical unit but more mathematical understanding. Decibel (dB) units are similar to percent (%), just different calculations and purposes. As a percent unit, so decibels are used to compare two quantities as the whole value in percents is expressed as 100%, so decibels are more complex, and it is a ratio of two independent quantities. Decibels are mostly used for energetic parameters like power or voltage and current. Decibel (dB), equal to 0.1 bel (B) . Bel – is a decimal logarithm of the ratio of two powers. If these powers P1 and P2, then the expression looks like this:
Regular ad hoc filters don’t guarantee optimal signal filtering as there are no criteria that evaluate filter characteristics. Usually, filter parameters are calculated empirically, and the best results do filtering. To avoid such a shortage, there are optimal filters used where some criteria optimize parameters. Optimal filtering’s main idea is to give bigger weight coefficients to signal spectra parts where signal noise has less power, and true signal spectral components have bigger power. Let’s project a simple Butterworth filter used as a comparative filter to optimal Wiener DSP filter.Butterworth filter transfer characteristics: Where N indicates filter Tap number. I will skip the Butterworth filter description as the main idea is constructing an optimal Wiener filter. Butterworth filter characteristics are pretty plain: The main disadvantage of the Butterworth filter is that signal is distorted on filter output. If you want minimal signal distortions it is better to use an optimal Wiener filter. Filter chart looks as follows: