added images edited

Author: biomurph

PulseSensor_C_Pi/PulseSensor_C_Pi.md

@@ -1,6 +1,5 @@
 # Pulse Sensor + C + Raspberry Pi
-The example code here is written in C to run on Raspberry Pi
-There are two programs. They both rely on the wiringPi library, which should have been included in your OS distribution. If not, go to [wiringPi](http://wiringpi.com/) to download it.
+The example code here is written in C to run on Raspberry Pi. There are two programs: **Pulse Sensor Timer** and **Pulse Sensor Gnuplot**. They both rely on the WiringPi library, which should have been included in your OS distribution. If not, go to [wiringPi](http://wiringpi.com/) to download it. You might want to update it while you're at it. Open a terminal window and type in `sudo get-apt update wiringPi`
 
 ## Things you'll need
 
@@ -11,23 +10,34 @@ There are two programs. They both rely on the wiringPi library, which should hav
 * LED & Resistor (220ohm - 1K)
 * Jumper wires (male/female)
 
-There are many was to set up your Pi. We used [Adafruit's](https://learn.adafruit.com/series/learn-raspberry-pi) tutorial to get set up. Once you have the Pi OS up and running, you will want to make sure that your configuration settings allow us to connect the Arduino. In the GUI, select `Raspberry Pi Configuration`, then open the `Interfaces` tab and enable Serial Port.
+There are many was to set up your Pi. We used [Adafruit's](https://learn.adafruit.com/series/learn-raspberry-pi) tutorial to get set up. Once you have the Pi OS up and running, you will want to make sure that your configuration settings allow us to connect to the hardware SPI bus. In the GUI, select `Raspberry Pi Configuration`, then open the `Interfaces` tab and enable SPI.
 
-![Conf_Window_Serial_Enable]()
+![ConfWindowSerial](../images/PiConfigWindowSPI.png)
 
 To do this on the command line, you need to edit your config file. Open a terminal window and type in
 
 	sudo raspi-config
 
-This will open up a configuration panel. Use the arrow keys to move down to `Interfacing Options` then press the right arrow to highlight `<Select>` and press either the space bar or Enter/Return. In the next pane, arrow down to the Serial Port option and enable it. Pi may ask you to reboot, so go ahead and do that, otherwise arrow your way to `<Finish>` and get out of the config menu.
+This will open up a configuration panel. Use the arrow keys to move down to `Interfacing Options` then press the right arrow to highlight `<Select>` and press either the space bar or Enter/Return. 
+
+![InterfaceOptions](../images/InterfacingOptions.png)
+
+In the next pane, arrow down to the SPI option and enable it.
+
+![EnableSerial](../images/EnableSPI.png)
+
+Pi may ask you to reboot, so go ahead and do that, otherwise arrow your way to `<Finish>` and get out of the config menu.
 
 
 ## Connect your Pulse Sensor to Raspberry Pi
 The Pulse Sensor outputs an analog signal, which the RasPi cannot natively handle. In the examples below, we are using an Analog to Digital Converter (ADC) IC to digitize the Pulse Sensor signal. As of this writing, the code below supports the MCP3008 ADC IC. (You could use the MCP3004 if you like). The Wiring Pi library has functions that enable us to easily access data from the MCP3008. You can pick one up at [Mouser](https://www.mouser.com/ProductDetail/Microchip-Technology/MCP3008-I-SL?qs=BYQkrObauiuZK6Atf%2FfReA%3D%3D&gclid=CjwKCAjwhbHlBRAMEiwAoDA343G0yGlECsWZ5zo-5UbrMk58sLaK11XtHWNU8w9fzKlpIiY343y0YBoCrBgQAvD_BwE) or [SparkFun](https://www.sparkfun.com/products/15099) or [Adafruit](https://www.adafruit.com/product/856). 
 
-The RasPi interfaces the MCP3008 via the hardware SPI bus. Here's a diagram to help you assemble the circuit. In addition to the MCP3008, you will need a [breadboard](https://www.adafruit.com/product/64) and some [male/female jumper cables](https://www.adafruit.com/product/826). We want to blink an LED, so you should have one of those handy, along with a resistor (220ohm to 1K should work fine).
+The RasPi interfaces the MCP3008 via the hardware SPI pins. Here's a diagram to help you assemble the circuit.
+
+![Fritzing Diagram](../images/PulseSensor_RasPi_MCP3008_fritz.png)
+
+In addition to the MCP3008, you will need a [breadboard](https://www.adafruit.com/product/64) and some [male/female jumper cables](https://www.adafruit.com/product/826). We want to blink an LED, so you should have one of those handy, along with a resistor (220ohm to 1K should work fine).
 
-![Fritzing Diagram]()
 
 ## Pulse Sensor Timer
 In order to get accurate BPM data from the Pulse Sensor, it is important to have fast and regular reading of the Pulse Sensor analog signal. By fast, we mean 500Hz (1 sample every 2 milliseconds). By regular, we mean 1 sample every 2 milliseconds. Period. Not 2.5 milliseconds, not 1.8 milliseconds, not whenever the OS decides to get around to it. This is much easier to do on a microcontroller where you are not running with an operating system. Arduino, for example, has no problem setting its hardware timer to sample data every 2 milliseconds on the dot. But we're not in Arduino, we're in RasPi, and things are different.