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  1. HellasTechn

    7805 regulator capacitors

    I have an 7805 regulator feeding a microcontroller for some very important project of mine. I have seen many different schematics of 7805 regulator circuits and i see that they use different capacitor values on the input and output pins of the 7805. My question is: how should i choose the input...
  2. HellasTechn

    Problem interfacing Arduino with an rs422 GPS receiver.

    Hello ! Im back here with yet an other mysterious problem. A couple of years ago i started building a project that involves an arduino mega and a GPS receiver that has RS422 output at 4800 bps baud rate. Unfortunately the arduino use serial communication TTL level. I have builded a pcb where...
  3. HellasTechn

    Help with Tektronix TDS-3012B Oscope

    Hello ! I Use a Tektronix TDS-3012B Oscope and i get this little strange behavior on both channel A and B. Even with no probe connected or with the probe connected and shorted to GND, i do get readings on the display that range from 0 to 100mv peak to peak. and from 0 to 400K frequency. like...
  4. HellasTechn

    Help select suitable Mosfet for driving relay.

    Hello ! I want to drive a DPDT relay (FEME LCA 002 12 57) from my arduino mega board. So far i used a BC337 transistor but after running it for a day or two having the relay continuously engaged, i found the transistor shorted. The relay coil will draw 45-50ma and has a resistance of 265 Ohms...
  5. HellasTechn

    Advice about MC34063 based buck converter diagram

    Hello to all forum members. I am working an a small project of mine that involves an arduino board and a few relays. My question has to do with the power supply section of my project.- The arduino board needs 5V to run and the relays 12V. I have a 12V 2A switching power supply. My intention is...
  6. HellasTechn

    Help with Arduino Serial communication.

    Dear friends. I am working on a project where an arduino uno and a GPS receiver are involved. The gps unit transmitts serial data NMEA. The data string on Hyperterminal looks like this : $GPGGA,123519,4807.038,N,01131.000,E,1,08,0.9,545.4,M,46.9,M,,*47...
  7. HellasTechn

    Programming languages and MC selection.

    Hello friends. I am new in the world of Microcontrollers. I want to learn a programming language and build a few projects i have in mind. I only know very little Picaxe BASIC language since i have used Picaxe chips 2-3 times. They are really nice and user friendly together with the software that...
  8. HellasTechn

    Question about using two SMPS.

    Hello !!! I am going to post a silly question but since i am not 100% sure i would like your advice. Can i use two identical smps 28V each to get symmetrical output (+28V) - (common) - (-28V) ? what should i consider ? I will explain further what i am trying to do and show pictures but i...
  9. HellasTechn

    ZOTEK ZT102 Multimeter.

    Hello people! I was looking for a multimeter and came across this ZOTEK ZT102. https://www.ebay.com/itm/Digital-Multimeter-6000-Counts-ZT102-Pocket-Mini-Auto-Ranging-Handheld-Tester/332711304405?hash=item4d77239cd5:g:QF0AAOSwJ89bPYrt Does it worth anything or is it just an other cheap...
  10. HellasTechn

    Tablet RF coaxial cable.

    Hello friends, its been long since my last post but now im back with an other question. Does anyone know the type of the rf cable is used within tablets to connect the WIFI antenna with the module ? I have googled but it is as if it has no name... I need to source several meters of it for a...
  11. HellasTechn

    Resistor Value.

    Hello ! Could someone please tell me the value of this resistor ? Colours right are : Brown, Black, Gold, Brown. The DMM reads 30.1Kohm but the resistor is slightly deformed and i am not sure if the value has shifted. THANKYOU.
  12. HellasTechn

    RS232 - RS422 CONVERTER

    HELLO ! I am looking for some converter that can convert rs232 to rs422 and at the same time rs422 back to rs232. In other words i need to connect the converter to my laptops rs232 serial port and exchange data between an rs422 device. Probably something that can be powered from a 5v usb port...
  13. HellasTechn

    Kenwood KA1030 audio amplifier problem

    Hello again ! The amplifier mentioned in the title was gifted to me by someone who doesnt want to keep it because it is not working. I am thinking to fix it and keep it as spare. When i pluged it in it would not turn on and no LED'd in front panel came on. I opened it and found the mains fuse...
  14. HellasTechn

    555 pwm controller.

    Hello friends. A colleague gave me a nail drill that was damaged (rpm stuck to max). I found the controller chip shorted and can not find a replacement anywhere (local stores-ebay-aliexpress). It uses an 1Amp transformer to bring 220V down to 18 and a bridge-capacitor circuit to make it DC. I...
  15. HellasTechn

    Huntron Tracker 2000.

    Good day dear friends, My wish to all of you for the new year is whatever is for your soul's best interest. Recently a device called Huntron Tracker 2000 came into my hands. I have no idea what that device is and what exactly it does or how. I Googled "huntron tracker 2000" and found out that...
  16. HellasTechn

    RS422 to RS232 converter.

    Good day ! I have been searching the net for some cheap RS422 to RS232 converter. While i have found tons of RS232 to RS422 converters, i have found none to do the opposite. Anyone have an idea where i can find one or a circuit diagram i could use to build one ? Thank You !
  17. HellasTechn

    Regulator question.

    Hello ! I have a few 78xx and & 79xx Vregulators. I suspect some of them are bad. The 78xx i test with my DMM and bench psu by connection the positive of the PSU to pin 1 , the negative to pin 2 and read output with my DMM from pin 2 to pin 3. I have an 7915 Vreg that i connect as follows ...
  18. HellasTechn

    USB to UART serial converter.

    No... i also had output scopings.
  19. HellasTechn

    Tank water level sensor.

    Hello friends ! Here i am today, thinking about my new project which is a water level sensor for a tank. I think it would not be that hard to write a code on a picaxe for such project but what sensor should i use ? On the web i have seen ultrasonic sensors for arduino used as water level...
  20. HellasTechn

    Help designing a 5V UPS circuit.

    Hello Friends. Here is my idea: i have a circuit that runs on 5Vdc and a 12V supply with an 7805Vreg feeding it. My idea is to make a "ups" with a 9V Nimh (200ma rechargeable) battery so that when the 12V are gone the circuit will be running from the 9V battery again through the 7805Vreg. My...
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