LM3S1968 – The Longhorn Engineer https://longhornengineer.com Robotics, Pinball, Hacking, Portables Tue, 20 Dec 2022 20:20:51 +0000 en-US hourly 1 LM3S1968: 74HCT595 Shift Registers https://longhornengineer.com/2011/11/08/lm3s1968-74hct595-shift-registers/ Tue, 08 Nov 2011 11:10:37 +0000 https://longhornengineer.com/?p=725 Continue reading LM3S1968: 74HCT595 Shift Registers →]]> For one of my up coming Labs for EE445L I am going to need to expand the I/O of the LM3S1968. I am using the 74HCT595 much like on my pinball machine. One 74HCT595 allows you to turn 3 output pins into 8 output pins. They can be daisy chained so you can have any multiple of 8 output pins for those 3 original output pins.

In this demo I have 3 74HCT595 chips wired up. Instead of using the SSIO ports on the LM3S1968 I bit banged the port. SSIO is built in hardware that does serial communication. I decided to not use is for the 74HCT595’s because I am going to use it in controlling a DAC.

http://www.youtube.com/watch?v=_bkljz3YN60

The code is fairly module and easy to change to different ports and pins.

Link to the code.

]]> EE445L : Lab 7 Temperature Data Acquisition System https://longhornengineer.com/2011/11/02/ee445l-lab-7-temperature-data-acquisition-system/ Thu, 03 Nov 2011 02:43:04 +0000 https://longhornengineer.com/?p=718 Continue reading EE445L : Lab 7 Temperature Data Acquisition System →]]> I am taking a class called EE445L which is microcontroller applications. It is a mainly lab based class where we design and prototype a new embedded system every week. We are using the Texas Instruments LM3S1968 Evaluation Board. The microcontroller is a ARM Cortex M3. It has an on board OLED display and a USB debugger. It is a fairly impressive piece of kit.

This is Lab 7 which is a Digital Thermometer. I can not post the code or schematics due to this being a Lab and it would be looked upon as academic dishonesty.

Lab 7 Problem Statement.

The Thermistor is a non linear device. That is as temperature increases linearly the resistance across does not scale linearly. Part of the circuit involves a resistor “bridge” this is a non linear setup. If you combine two non linear systems you can roughly get a linear system. It is not perfect but it is close enough.

After the bridge part the voltage level goes into an amplifier which boosts the signal to a level that the LM3S1968 can read via its ADC (Analog to Digital Convertor) ports. This signal is the passed through a Low Pass filter. The filter is set to cut off at 10Hz. The LM3S1968 is configured to sample at 100Hz. The signal is low passed to prevent aliasing from high frequencies which would cause interesting glitches on the ADC.

http://www.youtube.com/watch?v=prSfExM7wfY

I will be recording all the major EE445L labs in the next coming days.

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