Linking SCR triggering to a microprocessor for current control

Discussion in 'The Projects Forum' started by MrSmiles, Dec 12, 2011.

  1. MrSmiles

    Thread Starter New Member

    Nov 26, 2011
    I'm building a microprocessor based control of a SCR that will, through a program from the MPU, increase the conduction of the SCR in a controlled sequence.
    I am aware that I can do this with a photo-coupler diode triggering the SCR , but I'm still unsure of which MPU, MCU or (?) is best suited for this job. I've looked at several from different companies at, but I'm basically confused.
    This unit will have a 16 key keypad, a 20 digit display, and 10 inputs & outputs and enough memory to handle the SCR firing program and a monitoring program, probably total 100K for all.
    I looking for suggestions on what is a suitable, yet inexpensive MCU, MPU for this project, which comes with a programming software included with purchase.
  2. tracecom

    AAC Fanatic!

    Apr 16, 2010
    The only family I know of that meets this requirement is PICAXE. See their website; I think you will find the variety of sizes will more than meet your needs.
  3. jimkeith

    Active Member

    Oct 26, 2011
    My experience is with the intel 8051 series and derivatives, and ASM51 assembly software. This device is powerful enough to do phase control for three phases and have plenty of power (time and memory) remaining for acceleration and PI feedback compensation etc. While it appears to be on its way out, there are now numerous sources and each continues to bring out faster versions with flash memory and in-circuit programming etc.--since they run legacy firmware, usage remains high and price competitive. On the other hand, I do not believe that they are often used in new applications. Higher level languages do poorly on this platform as they run much slower and consume excessive code memory--cannot do this demanding task.

    It appears that the embedded microcontroller of choice is now the PIC as tracecom indicated in the previous post--while I have no experience with this device, I think that it has to be at least as powerful as the 8051 and derivatives. I have also heard that it is easy to use.

    For triggering SCR gates, I prefer pulse transformers as they provide fast gate rise times as well as isolation. Opto-couplers are OK, but isolated power is still required. A pulse train is preferable to single pulse to drive the gate transformer(s) as repetitive pulses will re-trigger the SCRs in case they are commutated via line disturbance etc, or if the initial pulse occurs before the SCR is forward biased.
  4. thatoneguy

    AAC Fanatic!

    Feb 19, 2009
    The PICAXE is about the only one that has the development environment, and they make lots of versions.

    Through Multiplexing the keypad and display will bring down the I/O a great deal.

    Call it 8 pins for keypad (4x4), 2 pins for display (serial shift registers for LCD or LED displays) 10 for I/O and the 28M2 or 28X2 will have the speed and memory you need. The 40 pin M2 or X2 will also suffice and give you an extra dozen+ I/O

    The shift registers and display would need to be built on a separate board, as would the keypad, unless you design a PCB specifically for this option. Commercial PCB created typically for over 12 units being made is where homemade PCB vs. professional PCB become affordable.
    Last edited: Dec 12, 2011