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  1. HellasTechn

    Optocoupler & mcu

    Hello everyone ! My latest project involves a micro controller and a solenoid that works with 220VAC. Once the solenoid gets the 220VAC on its coil, it opens for a few seconds. My goal is to count how many times the solenoid opens. I Think that i can use a bridge rectifier and an optocoupler to...
  2. HellasTechn

    Opamp test circuit.

    Hello everyone. today i was thinking of a test circuit for opamps like the 741. i made a diagram. What do you think of it ? Thanks !
  3. HellasTechn

    Diving into JTAG

    Hello everyone, the past few days i got my hands on two very nice tools that i would like to get to learn how to use. 1st is an ABI JTAG master and the 2nd is a JTAGULATOR board. There are videos on youtube about JTAG and JTAGULATOR but since i have never used tools like these before and it's my...
  4. HellasTechn

    Opinion about selling value of old turntable and broadcast receiver.

    Hello people, how are ya all doing ? I have two very old pieces of equipment that i am thinking to sell but i have no idea of their value. First is a portable turntable National 2-band 12-transistor radiograph HG-720 probably manufactured between years 1962-1964. It is in geed cosmetic...
  5. HellasTechn

    Testing Operational Amplifiers

    Hello everyone, I have two components i would like to know how to test. Both are opamps and theoretically the same. 1st is an lm741h and the 2nd is an lm747h. Both are in metal can packages. How can i test them to verify that they work correctly? Thank you !!!
  6. HellasTechn

    RS232/485 & UART

    Hello everyone, i hope you are all doing good ! I have question that will probably sound strange to you. A few years ago i made a circuit with a microcontroller that reads RS422/485 serial data passing through an RS485 to UART transceiver chip (in receiver mode) and an other circuit that reads...
  7. HellasTechn

    VGA vsDVI

    Good evening everyone! I have a question concerning my pc’s connection to my monitor. I have an old PC with an nvidia geforce GT640 card and an LG flatron L1970hq monitor. My monitor supports only VGA and DVI. With the VGA connection I can use max resolution (1280x1024) at 75hz refresh rate but...
  8. HellasTechn

    Any info on these old chips ?

    Hello ! Iv'e got my hands on an old PCB haveing a number of IC's on it. For most of them i found the datasheets online but i have four that i can not find. Here is a picture of them : Markings are : a)Ti 527 b)Ti TL710MJ c)6330-1J d)7483N7720 Thank you :)
  9. HellasTechn

    LM1117 linear regulator.

    Greetings dear forum members. Today i am considering a power supply for a microcontroller. In particular one that will implement an LM1117 regulator the TO-252 package. In the past i have used the 7805 regulator many times and i am pretty familiar with its cooling requirements but when it comes...
  10. HellasTechn

    RS422/485 and ground wire.

    Greetings dear friends. Today I was reading about RS422/485 protocols. I do know that these are differential line but that raise a question. Do they really need an extra signal ground wire or not ? Ive seen it many times used without a ground wire, just the data + and data- lines. How does the...
  11. HellasTechn

    What to do with all these chips?

    Good day dear friends, happy Μonday ! Today I am posting something different for a change. Over the past decade many different kinds of boards have fallen into my hands for salvaging chips. Whenever I was in the mood and had enough time I would strip them and list the chips ive removed. I now...
  12. HellasTechn

    Help recovering fdd with bad sectors LINUX or Windows

    Good day everyone. I found a box with old floppy disks dating back to 90's and wanted to copy them to my pc. I have a set of windows 3.1 setup disks and one of them has bad sectors (disk 2). I switched to linux debian jessie because windows10 and scandisk does not work with this fdd. So i...
  13. HellasTechn

    RF keyfob & arduino.

    Hello ! I have a small motor that i want to control with an arduino (uno or mega) using an RF keyfob. simple operations like start and stop. Nothing special. I really have no idea about how RF keyfobs can work with arduino. Could someone point me to some rf module and maybe give me some insight...
  14. HellasTechn

    UltraSonic Transducer.

    Hello everyone, Like i mentioned in my other post here : https://www.electronicspoint.com/forums/threads/creating-a-user-interface-for-arduino.292520/#post-1795054 I want to build my own arduino based fuel injector cleaner. Further more i have seen theese ultrasonic cleaners that work pretty...
  15. HellasTechn

    Creating a user interface for arduino.

    Hello friends, I was working on my car when i came across a few YouTube videos of DIY fuel injector cleaning methods. Since i was looking for a new project to study i decided to build my own arduino based fuel injector cleaner. I know how to handle my analog/digital inputs/outputs to execute the...
  16. HellasTechn

    Question concerning Arduino and C++

    Hello friends. I am new to programing and microcontrollers in general. I had no knowledge of C language until I recently found some very useful YouTube lessons about C language and how to build a small program on PC with it. After watching the lessons i managed to understand the very basic...
  17. HellasTechn

    Two relays in series with flyback diode.

    My question has to do wth the flyback diode in the below described circuit. I have two relays in serries (6V coil each) that are connected to a 12V source and controlled via a logic gate mosfet. I know that a flyback diode has to be placed as close th the relay's coil as close as possible but...
  18. HellasTechn

    Help understanding SMD PPTC fuse specs.

    Hello everyone. I have this question now that i need help with. I have a GPS with an rs422 output. I want to protect its output from burning if short circuited to ground. According to the RS422 standard the RS422 lines have a max 150ma short circuit current. I want to use fuses in serire with...
  19. HellasTechn

    how much current from RS422 output.

    Hello everyone and Merry christmas. I have this strange question. In the past i accidently shorted the rs422 output of a driver chip and it got damaged. can i avoid it by placing a fuse in serries ? how much current can a typical rs422 driver deliver before it gets damaged ? I try to figure...
  20. HellasTechn

    DPDT relay lifespan.

    Good day everyone. I have a question concerning some relays i use for a project. I have been searching the datasheet to find the average lifespan in hours of the relays coil under DC voltage. The relay i use is the SCHRACK RT424012 and the voltage applied on its coil is 12V. Here is a link to...
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