IC and Sockets
The ATMEGA8A-PU is a high-performance, low-power 8-bit AVR RISC-based Microcontroller combines 8kb ISP flash memory with read-while-write capabilities, 512B EEPROM, 23 general purpose I/O lines, 32 general purpose working registers, three flexible timer/counters with compare modes, internal and external interrupts, serial programmable USART, a byte oriented two-wire serial interface, 6-channel 10-bit A/D converter (8-channel in TQFP and QFN/MLF packages), programmable watchdog timer with internal oscillator, SPI serial port and five software selectable power saving modes. The device operates between 2.7 to 5.5V. By executing powerful instructions in a single clock cycle, the device achieves throughputs approaching 1 MIPS per MHz, balancing power consumption and processing speed.
- High-performance, Low-power AVR® 8-Bit Microcontroller
- Advanced RISC Architecture
- High Endurance Non-volatile Memory Segments
- Atmel QTouch® Library Support
- Power-on Reset and Programmable Brown-out Detection
- Internal Calibrated RC Oscillator
- External and Internal Interrupt Sources
- Idle, ADC Noise Reduction, Power-save, Power-down and Standby Sleep Modes
- 2.7 to 5.5V, 0 to 16MHz Operating Voltage
- 3.6mA Active, 1.0mA Idle Mode and 0.5µA Power-down Mode Power Consumption
Applications:
Building Automation, Consumer Electronics, Motor Drive & Control, Industrial, Automation & Process Control, Metering
The Raspberry Pi is a great computer but there's just one thing that most hardware hackers will find missing: a few inputs for connecting analog sensors. This is where the MCP3008 chip comes in handy, with eight 10-bit channels accessible over SPI. Thanks to the Raspberry Pi's SPI interfaces and its two 'Chip Select' pins available off of the main GPIO connector, the problem is solved.
Features
- 10-bit resolution
- ± 1 LSB max DNL
- ± 1 LSB max INL
- 8 input channels
- Analog inputs programmable as single-ended or pseudo-differential pairs
- On-chip sample and hold
- SPI serial interface (modes 0,0 and 1,1)
- Single supply operation: 2.7V - 5.5V
- 200 ksps max. sampling rate at VDD=5V
- 75 ksps max. sampling rate at VDD=2.7V
- Low power CMOS technology
- 5 nA typical standby current, 2 µA max.
- 500 µA max. active current at 5V
- Industrial temp range: -40°C to +85°C
Applications
- Sensor Interface
- Process Control
- Data Acquisition
- Battery Operated Systems
How-To
The following sample assumes that you're running the latest official Raspbian distribution, that you're logged in as root and that you haven't yet customized Raspbian to use SPI from a Python script. By default, the kernel module managing SPI communications is not loaded on Raspbian, so let's ensure that the 'spidev' device is available.
[email protected]:/# lsmod Module Size Used by snd_bcm2835 12808 0 snd_pcm 74834 1 snd_bcm2835 snd_seq 52536 0 snd_timer 19698 2 snd_seq,snd_pcm snd_seq_device 6300 1 snd_seq snd 52489 5 snd_seq_device,snd_timer,snd_seq,snd_pcm,snd_bcm2835 snd_page_alloc 4951 1 snd_pcm
If 'spidev' device is not listed, we need to remove it from the kernel module 'blacklist' so that it's automatically loaded on the next boot:
[email protected]:/# nano /etc/modprobe.d/raspi-blacklist.conf
Put a hash character in front of the 'blacklist spi-bcm2708' statement and save the file:
#blacklist spi-bcm2708
then, manually load the SPI device:
[email protected]:/# modprobe spidev
The command should just complete without returning an error. Validate the list of modules:
[email protected]:/# lsmod Module Size Used by spi_bcm2708 4401 0 spidev 5136 0 snd_bcm2835 12808 0 snd_pcm 74834 1 snd_bcm2835 snd_seq 52536 0 snd_timer 19698 2 snd_seq,snd_pcm snd_seq_device 6300 1 snd_seq snd 52489 5 snd_seq_device,snd_timer,snd_seq,snd_pcm,snd_bcm2835 snd_page_alloc 4951 1 snd_pcm
The 'spidev' device should now be available.
Next, install the 'git' package. It will be needed to install other packages from Github.
apt-get install git-core
Install the 'python-dev' package. It will be needed to compile the 'py-spidev' package.
apt-get install python-dev
Download and compile the 'py-spidev' package.
[email protected]:/# cd /home [email protected]:/home# git clone git://github.com/doceme/py-spidev [email protected]:/home# cd py-spidev/ [email protected]:/home# python setup.py install
At this point, SPI is available from Python 2.7. Assuming that you have wired the MCP3008 to the Raspberry Pi's SPI bus using CE0 as the 'chip select' pin, you can read all eight analog inputs using the following Python script.
[email protected]:/home# nano adc.py
Paste the script below in the editor and save it.
import spidev
import time
spi = spidev.SpiDev()
spi.open(0,0)
# read SPI data from MCP3008 chip, 8 possible adc's (0 thru 7)
def readadc(adcnum):
if ((adcnum > 7) or (adcnum < 0)):
return -1
r = spi.xfer2([1,(8+adcnum)<<4,0])
adcout = ((r[1]&3) << 8) + r[2]
return adcout
while True:
for adcInput in range(0,8):
print "ADC(", adcInput,")=", readadc(adcInput)
time.sleep(1) To execute the script
[email protected]:/home# python adc.py
Sample output using a 10K Ohm trimpot connected to the ADC's pin 3 and all other pins pulled down to ground using a 10k resistor.
ADC( 0 )= 0 ADC( 1 )= 0 ADC( 2 )= 0 ADC( 3 )= 507 ADC( 4 )= 0 ADC( 5 )= 0 ADC( 6 )= 0 ADC( 7 )= 0
Credits go to Jeremy for his work on the 'py-spidev' Python module which makes working with the MCP3008 straight forward. Alternatively, checkout wiringPi's SPI functions if you prefer using a 'C' API.
Related Tutorials & Samples
74HC 595N IC
Bits: 8
Pin: 16
Logic family: HC
Logical function: shift register
Output type: 3-State
Propagation delay time: 285ns
Operating supply voltage (Typ): 2.5V / 3.3V / 5V
Operating temperature: -55°C ~ 125°C
Operating supply voltage (Min): 2V
Operating supply voltage (Max): 6V
Integrated circuit with small size and light weight, high reliability for improving the reliability of equipment.
Package includes:
1 x 74HC595N 8 bit shift register IC
Driving the Shift register
Color: black
Number of pins: 28 pins (14pins / row x 2 rows)
Pin length: 2.9mm
Pitch: 2.54mm
Row to row distance: 7.62mm
Dimension: 35 x 10 x 8mm (L x W x H)
Contact termination through hole
Contact type dual wipe contact
Package includes:
1 x 28 Pins IC Sockets
Color: black
Number of pins: 8 pins
Pin length: 2.9mm
Pitch: 2.54mm
Row to row distance: 7.62mm
Dimension: 10mm x 10mm x 8mm (L x W x H)
Contact termination through hole
Contact type dual wipe contact
Package includes:
1 x 8 Pin IC sockets
1 x Circular hole 16 pin IC socket
- Timing from microseconds to hours
- A stable or monostable operation
- Adjustable duty cycle
- TTL compatible output can sink or source up to 200mA
Applications
Clock & Timing, Consumer Electronics, Aerospace, Defence, Military, Embedded Design & Development
Resources:
Some Projects
Overview
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