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Monday, August 19, 2019

Digital Interface Basics

After a long time a thread of discussion. It is about digital interfacing of embedded system. Only Education Points listed. Initials and country of origin also will not be mentioned henceforth.

When this Circuits FAQ started decades back around 2000, It was a PHP mail form called "Problems and Solutions". The mail was coming like 3-4 every day.

Question

Hello Sir. I am looking for someone that can help me with simple challenges from time to time, deciding on best electrical components and designing wired circuit diagrams to my specifications. Thank you!"

Only the delabs Answers are Reproduced Here

The output logic of your embedded system port bit (one pin) goes high  it can drive a drive a ULN2003A. - The output of this is open collector and can operate relays or lamps.

Using the ULN2003A

The Proximity Sensor can be turned on with an external PNP power transistor if the current consumption of that is above 300mA. It is not a good idea to heat The ULN2003A chip too much. Keep the return paths of these to a separate but linked ground as they carry more current.

If you are running short of ports in the Embedded System. Latch the Output by using 74HCT373. There may be logic level comparability problems check your Embedded System Supply. There may be ground loop problems.

Use ULN to drive PNP Transistor and things like a Relay, Lamp or your Proximity Switch.

It is important to learn and do things, this is the real electronics.  Do not overload any device, study current and voltage ratings. Keep Mains HV and High Current circuits that are dangerous in another card with optoisolaters.

Isolation Resistance and Insulation Resistance

message: what is insulation and isolation resistance, why and how it is measured? what are the consequences if it is not measured? 2008


Isolation Resistance and Insulation Resistance are both related to each other. Isolation Resistance could be in Giga Ohms and Tera Ohms and includes Surface Resistivity.

Insulation Resistance will be in the Range of Mega Ohms and Giga Ohms. You could say Isolation Resistance is a Tera Ohm and Giga Ohm Measurement Test.

Isolation Resistance and Insulation Resistance

Les us assume a 5KV Isolation Opto-Coupler on a Glass Epoxy PCB. You could Measure its Isolation or Insulation Resistance and it will be in the range of 1 Tera Ohms in a good PCB.

A good PCB will have a Slot Routed below the Opto Coupler for High Isolation. This will ensure Dust and Grime along with Moisture will not form a Leakage path below opto-coupler.

Use a Megohmmeter for Insulation Resistance of Transformers, Coils and Relays. Use a Teraohm Meter to measure Isolation Resistance in Opto Couplers, PCB, Ceramics and Capacitors.

Megohmmeter is a special type of ohmmeter used to measure the electrical resistance of insulators. Insulating components, for example cable jackets, must be tested for their insulation strength at the time of commissioning and as part of maintenance of high voltage electrical equipment and installations.

6520 Programmable Teraohmmeter makes resistance measurements up to 10 PΩ. Whether used in automated mode via the Guildline developed TeraCal Software or as a stand-alone meter,

DC Small Motor Control using PWM

message: Greetings, I have a kit motor controller. I works just fine. It uses the NE556. I read some where ( on a NE555 )that I can change one of the capacitors with a variable capacitor to get the full range of frequencies out of the NE555.

 Is it possible to get adjustable frequencies out of the NE556? I have the circuit drawing. Is there any one I can send the diagram to so they could tell me which capacitor I can change? Thank you,

BR USA


PWM DC Motor Speed Control - This is a circuit for controlling the speed of small DC motors, it works nicely as a speed controller for an HO or N gauge model railroad.

DC Motor Control for Low Power

Timing 555 Motor Speed - It uses a variable frequency 555 astable. The astable triggers a monostable that produces pulses of a fixed width. At lower frequencies, the monostable pulses are infrequent and the output is high about 20% of the time.

delabs