The Security Guard duty monitor below, shown in eight circuits at Digital Circuits – 1 are examples of logic circuits, i have converted them from the DOS Orcad to Orcad 9 and corrected some errors a few years back.
These circuits can be used for looking at the logic blocks or to learn. This product was built and sold to some firms many years back. Now these designs are best done with a PIC or Atmel chip. Here is the user manual Electronic Shift Monitor ESM9000
I don’t remember if this circuit worked properly. But a few were made and i might not have shown the modifications that were done to make it work. This was meant to be a portable, low cost, insulation tester for an electrician. If you try it out and debug it it may work well. A negative voltage is derived by shifting gnd with two diodes, i feel this did not work very well. Two pins of CD4028 pins are also used to boost the reference to get two extra ranges as 4051 has a 100E on resistance. From Schematics of Read More …
I had to once interface an high voltage circuit to PC, The uC had to communicate thru RS232–Comm port–Serial Port. Even though i had isolation at the sensors and actuators to make doubly sure the PC also has been isolated. There are chips that are available for this purpose, The circuit above is built with discrete and passive components except for the opto 4N35. You can use MCT2E and CNY17-3 Optos too. For MCT2E some tweak may be needed as current transfer ratio is 20, for the other two CTR is 100 so above design will work. The circuit derives Read More …
I wanted to design a logic probe as a tutorial, but there were many good ones in the web so i have tried to design a single digit voltmeter. This circuit is a design, i am unable to test it now, later if i test it and find mistakes i will update this page. You can help me by pointing out the errors. First bear it in mind that it is a single digit voltmeter which is 0-9 counts only on the positive side, that is it can measure +0 to +9V DC +/- 1V error. That may not be Read More …
This circuit is a small representation of a very low cost printer sharer i made very long ago. This is as much i can remember of the basic ideas behind the product. I used to pot the product in epoxy with a black dye and sold a few, they sort of served the purpose. Output impedance of this circuit is high, sink is 220K source is 3.9K+ so use some buffers or drivers at Output. when Enable A is at float-high impedance or low the output O1-O4 is not influenced by A1-A4 inputs. If Enable A is made logic high Read More …
A, B, and C are the Digital Control for x, y and z input and output pairs.The voltage at Vinx is stored in C1 when A goes high, when A is low the voltage stored in C1 is read by buffer U2A. The stby or standby input should be low when sample and hold is operating. If stby is taken high then C1 Cap is isolated and leakage is minimum. The supply of +/- 7.5V is chosen as OFF resistance of 4053 is high at this supply.
CD4538 is a dual Monostable Multivibrator. When you trigger the chip the output sends off one single pulse or one high-low event. The T+ pin 4 of U1a is the positive edge trigger or raising edge trigger input, the T- pin 5 is falling edge or negative edge trigger input. Now see the image of the single pulse above which shows both the edges, If this is the input pulse at pin 5 then the falling edge turns the output pin 6 from low to high, this output remains high for time T = R2 * C1 and then goes Read More …