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Monday, February 28, 2011

AM Radio Receiver using 555: Simple RF

We found a nice 555 based AM radio with improved designed by Eric for his 555 Timer Contest Entry.
[Source: http://tubetime.us/?p=85]
The best part is the new demodulation circuit used.
[Source: http://tubetime.us/?p=85 ]
Here is the Description of the Circuit:
The AM radio signal is tuned by inductor L, which is 300 turns of wire on a 1/2 inch diameter cardboard tube made out of an old toilet paper roll, along with the 100pF variable capacitor. One end of the parallel configuration of L and C connects to an antenna (surprisingly long!) and the other end connects to a ground wire which is tied to the AC outlet ground (old books tell you to ground it to a water pipe). So far this is exactly like an AM crystal radio.
The 555 timer is configured as a pulse width modulator in a non-traditional configuration. If I used the standard approach and connected the input to the CV pin, the low impedance of the pin would prevent the circuit from receiving any radio signals. I had to invert the circuit and tie both high impedance analog pins, Threshold and Trigger to the radio signal input. This is the reason why the CMOS version of the 555 timer performs much better than the standard bipolar, which has higher input bias current.
The pulse width modulator ramp is created by the 0.01uF capacitor and the 10K bias potentiometer which are connected to the Discharge pin. The potentiometer wiper goes to the LC arrangement. With no radio signal coming in, the voltage on Threshold/Trigger ramps up until it hits the threshold, and then Discharge causes the voltage to ramp down again.
When a radio signal comes in, it gets superimposed on the ramp signal, causing the threshold and trigger comparators to trip early or late in a cycle. This variation causes the output duty cycle to vary, which we can hear as sound in the speaker.
Demodulating the signal properly requires adjustment of the bias knob, so that part of the radio   signal is “clipped” and ignored by either the threshold or trigger comparators. This ensures that    the negative “halves” of the radio wave don’t cancel out the positive “halves”.
The circuit uses the ICM7555 which is the CMOS version for the original NE555 and also eliminates the issue of low impedance on the 'Threshold' and 'Trigger' pins of the timer IC.
We congratulate Eric on his innovative creations and wish him best of luck for the 555Contest.

For Further Info visit:

Friday, February 11, 2011

mbed a world of things: Intersting Links

Here are a few interesting links from mbed that might be helpful in case there are any of your ideas on the same lines:
  1. SD Card Cookbook Page Showing the File System Driver for SD Cards on mbed
  2. SD File System Driver for the SD Cards Interfacing on mbed (LIB)
  3. SD Card Tests - Test showing how many SD cards can work with mbed
  4. ADC Driver by Simon Blandford which gives direct low level access for ADC and is a better implementation than the AnalogIn.
  5. Reference Design for new Hardware based on mbed's microcontroller LPC1738
  6. Prototype-to-hardware a guide to help in programming the external LPC1738 microcontroller boards
  7. Eagle Libs for mbed. (EAGLE)
  8. SDHCFileSystem to Support upto 32GB (CODE)
  9. EthernetNetIf - Ethernet Interfacing Library (LIB)
  10. HTTPClient - HTTP Client Library also used in twitter example (LIB)
  11. BlueUSB - Bluetooth support for MBED with $2 Bluetooth dongles. Includes a USB host and built in support for bluetooth HID devices such as mice, keyboards and wii controllers. (CODE)
  12. MSCUsbHost - Implementation of USB Host for mbed 1768 which can access USB flash drives. See Igor Skochinsky notebook page for details.(CODE)
  13. NetTool - A low-level network debugging utility that utilizes raw packet i/o to construct and deconstruct tcp, udp, ipv4, arp, and icmp packets over ethernet.(CODE)
  14. EthernetTester - Basic Ethernet Testing program and documentation by Michael Wei (CODE)
  15. ethspam - A program shows how to send an Ethernet packet. It simply sends ARP Who is messages for every IP. (CODE)
  16. ethsnif - A simple Ethernet sniffer - demonstration how to use the Ethernet interface by transmitting all the packets received over the USB serial port to PC. (CODE)

Friday, February 4, 2011

AVR Programmer ISP: STK200 using Old PC Hard Disk PATA port

We found this awesome cheap technique to convert you PC Hard Disk port into Parallel Port and then use it as STK200 for programming AVR. This is made possible in Linux - well the hacker's friend.
Courtesy: Hackaday.com
This implementation uses a few NOR gates, Transparent Latch and a Tristate Buffer. Here is picture of the Implementation circuit.
Courtesy: ircjunk
The configuration of the programmer is such that you can have it as a Slave or a Master and configure it depending on that. All it needs is a simple remapping of the PC parallel port kernel driver in linux.
Here are the ATA port address:
0x1F0 - Primary Master ( Not preferred since you might have your HDD attached here)
0x3F6 - Primary Slave
0x170 - Secondary Master
0x378 - Secondary Slave

Then in linux its just a sequence of commands:
rmmod partport_pc
modprobe parport_pc io=0x170 irq=none,none,none
(For location of the programmer on the Secondary Master port 0x170)
Linux doesn't like this might throw up some error messages.

Thats all your port is now remapped and the simple AVRdude command works:
avrdude -p m32 -U lfuse:w:0xe2:m -U hfuse:w:0xd8:m

To find more read the following links:

Here is a picture of the Finished build real close:
Courtesy: ircjunk
We congratulate Rue on this innovative creation.