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1  Using Arduino / Motors, Mechanics, and Power / Soleniod for bell stricker? on: July 02, 2014, 03:22:15 pm
I am making a clock project and am hoping to interoperate an alarm bell into it. I was wondering if anybody knew where I could start looking for solenoids to use as a striker for the alarm. I have 12V at my disposal and would require a medium switching frequency, ie enough to strike the bell a couple of times a second.
2  Topics / Product Design / Arduino Logo for eagle on: June 30, 2014, 01:59:33 pm
Does anyone have an eagle library with the arduino logo for a the silkscreen (tPlace I think)? If I can't find one, I'll rip it from one of the board files and make a whole logo library myself, but I thought I'd check here before starting.
3  Topics / Product Design / Re: Designing shields on: June 30, 2014, 01:31:04 pm
There's a shield for that:
http://mayhewlabs.com/products/go-between-shield
4  Using Arduino / General Electronics / Re: Mosfet controlling a power supply on: June 27, 2014, 06:38:02 pm
Quote
Many switchmode chips already have a "disable" input to switch them on or off.
That was my initial idea before I started looking at MOSFETs, but the chip is the MC34063 that unusually doesn't have an output enable pin smiley-sad , the only time I have actually needed one as well...

edit: Do you think the supply will generate back emf when I unload it, and will I need anything more complex than a diode to cope with/absorb it?
5  Using Arduino / General Electronics / Re: Mosfet controlling a power supply on: June 27, 2014, 05:56:48 pm
I researched and understood what you said about low side switching, so I changed the entire design around to use a p-type (I had to use a transistor drive as I couldn't find any suitable logic level p-type MOSFETs, do you think it will work now?
6  Using Arduino / General Electronics / Re: Dimming problem with custom LEDS array modules on: June 27, 2014, 02:44:49 pm
I was assuming Vf=2V for the LED's, which is 'average' for most LED's bar white ones. I forgot about the 1V darlington drop, silly me.
7  Using Arduino / General Electronics / Re: Dimming problem with custom LEDS array modules on: June 27, 2014, 02:32:45 pm
Hey there, looking at your schematic (Its working for me btw) I see you have no resistors installed, in fact I am surprised that your LEDs or transistor array are not fried yet! As you are using a 3.3v supply this will be working to your advantage, but each darlington will still have to be dropping 1.3v! Install a 220 ohm resistor in series with each led (do not use one common resistor unless you only have one LED on at a time) and that should sort out the dimming problem, however the LEDs will be overall less bright.
8  Using Arduino / General Electronics / Re: Mosfet controlling a power supply on: June 27, 2014, 01:53:25 pm
Thanks for your help, I've looked around for some logic level MOSFETs, these ones seem perfectly suitable, and :
FDD24AN06LA0_F085: http://www.fairchildsemi.com/ds/FD/FDD24AN06L_F085.pdf Vgs=5v, Rds = 20mOhms
or STP55NF06L: http://www.st.com/web/en/resource/technical/document/datasheet/CD00002690.pdf,
I realise now that the L suffix on the end refers to logic level, I take it I'd waste a fair bit of power if I tried to turn on the mosfet rated for Vgs=10V with only 5V.

Quote
You've chosen a low-side switch here - is that OK - the ground side of the
PSU will be at 12V if you do this.

What do you mean by this, when the MOSFET is on doesn't the drain get tied to source (albeit with a tiny Rds), and when off isn't the Rds infinite?

edit: The supply which I will switching is this one: http://www.ebay.co.uk/itm/Nixie-tubes-Magic-eye-tubes-power-supply-module-kit-/261169220982?pt=Vintage_Electronics_R2&hash=item3ccee60d76, its a 35kHZ switch mode supply, 180V, 5W output. Input 10-18V, I have it running from 12V at the moment.
9  Using Arduino / General Electronics / Mosfet controlling a power supply on: June 27, 2014, 11:04:43 am
I'm building a circuit of which part of the secondary functions is to control a high voltage power supply using a mosfet. I've looked around for anybody who has done a similar sort of thing, but typing 'mosfet power control' into Google yields pages of switch mode supply schematics.  I've attached what I think is the correct form of the circuit, but as I'm only using an arduino, I am driving the gate to a high of 5V only, which I don't think will be enough, as the datasheet for the IRFZ44N specifies that 10V is required to have the 17.5 milli-ohm on resistance (but at 10A drain current). I do have access to +12v on the board, so could set up a transistor pre-drive stage for the fet if this becomes a problem. The power supply I will be driving is 5W output, and specifies a 85% efficiency when driven @ 12V, so 6.25W (on the low eff. side (80%)) input power. As I'll be driving less than 2A, will the 5v vs 12v gate voltage make a difference?
10  Topics / Home Automation and Networked Objects / Re: door opening with arduino and SIM900 on: April 28, 2013, 08:44:03 am
To interface with the SIM900, will require the at commands http://www.simcom.us/act_admin/supportfile/SIM900_ATC_V1.00.pdf, to read the text message you can use the command AT+CMGR, and serialRead to get the reply. To control the servo use the servo library (http://arduino.cc/en/Reference/Servo) and an 'if' statement on the read serial data.
I got a sim900 module last September but have not got round to using it extensively yet, (maybe summer). Here is blog which details use of a TC35 gsm modem, which uses most of the same commands as the sim900, http://denhart.dk/2012/01/21/siemens-tc35-gsm-module-arduino/. Hope this helps.
11  Using Arduino / Programming Questions / Shiftout 11-bit on: April 28, 2013, 08:14:03 am
I am thinking about using a digital volume control chip the U2429 by unisonic to control volume http://www.unisonic.com.tw/datasheet/U2429.pdf, but to control it requires a 11-bit data format (=2047) (7 data + 4 begin/end bits). The shiftout function only supports 8bit shifting (=255),  but is there a way to change it to operate upto 11bit, one way I thought of would be to shift the first 2 bits (channel select which i'll never alter), then the 7 data bits + 1 end bit and then finally the second end bit all separately, but the clock would interfere with control for the first and last sections, B00000001, BXXXXXXX1, B10000000. Anybody got any ideas apart from manually banging out the start and stops, and shifting out data?
12  Using Arduino / Project Guidance / Re: Resistors on: April 14, 2012, 08:59:27 am
There is only only one kind of resistor, you can limit both voltage and current, it depends how you wire them up. If they're in series you create a Voltage Divider, if in parallel you create a current divider.

http://www.kpsec.freeuk.com/resistan.htm
13  Using Arduino / Project Guidance / Re: PS/2 keyboard + LCD wireless communicator on: April 14, 2012, 06:02:05 am
I realised my error as soon as I posted. Here is my completly amended code.

Code:
/*
*****************
Woozle - 2012
*****************
*/
#include <LiquidCrystal.h>    //LCD libary
#include <PS2Keyboard.h>      //PS2 libary
String buff;                  // Buffer for PS/2 data
LiquidCrystal lcd(10, 9, 5, 6, 7, 8);  //LCD initialize
PS2Keyboard kb;                        //Keyboard initialize

void setup()
{
  kb.begin(4, 3);          // Set up the keyboard
  lcd.begin(16, 2);        // Set up the LCD
  Serial.begin(9600);      // Start Serial at 9600bps
}

void loop()
{
 
  if (Serial.available())     // Check if data is available
  {   
    delay(100);        // Wait for all data to arrive from PC
    lcd.setCursor(0,0);
    lcd.write("                ");       // Clear LCD top line
    lcd.setCursor(0,0);
    while(Serial.available() > 0) // While data is available
    { 
      lcd.write(Serial.read());    // Write it to screen
    }
  }
   if (kb.available())   // Check for incoming keyboard keystrokes
   { 
     
     char x = kb.read();   
     unsigned int y = buff.length();    //Length of buffer
     if (x == PS2_ENTER)                   //If return key is pressed
     {
      Serial.println(buff);                // Send the buffer over serial
      lcd.setCursor(0,1);                  // Set the cursor on bottom line
      lcd.write("                ");       // Clear LCD bottom line
      buff = "";                           // Clear the buffer
     }
    else
     {
      buff.concat(x);      // Add variable to end of string     
      lcd.setCursor(y,1);        //Postition that PS/2 data will be written to
      lcd.write(x);              // Send to LCD
     }
   }
}
I used 'l' for the next part. It has now been changed to 'y' because I got it mixed up with a 1. I don't know how to erase the last character of a String though so I have not been able to get the 'backsparce' working. Any ideas?
14  Using Arduino / Project Guidance / Re: PS/2 keyboard + LCD wireless communicator on: April 13, 2012, 06:59:43 am
Ok, so I have started editing the code, debugging as I went along along and already I seem to have a problem. I started by just setting up buffer as a string and by setting up the Return key to send the buffer over serial. But the data appears to the LCD as black filled-in boxes and when return is pressed the Buffer appears as the correct length of characters but all as 'ΓΏ's.
Code:
#include <LiquidCrystal.h>    //LCD libary
#include <PS2Keyboard.h>      //PS2 libary
String buff;        // Buffer for PS/2 data
LiquidCrystal lcd(10, 9, 5, 6, 7, 8);  //LCD initialize
PS2Keyboard kb;                        //Keyboard initialize
//Same here as before
if (kb.available())   // Check for incoming keyboard keystrokes
   { 
     char x = kb.read();  // Write keystrokes to a variable
     
     if (x == PS2_ENTER)
     {
      Serial.print(buff);
     }
     
     else
     {
      char x = kb.read();  // Write keystrokes to a variable
      buff.concat(x);      // Add variable to end of string
      byte l = buff.length();    //Length of buffer
      lcd.print(x);     // Send to LCD
     }
   }

Any ideas on why this is happening?
15  Using Arduino / Project Guidance / Re: PS/2 keyboard + LCD wireless communicator on: April 13, 2012, 05:39:42 am
Thank you, thats just what I needed, I will edit the code now and repost it when I have done it.
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