Project Definition

Project Description

This project was created part of a two-term senior design course sequence in Electrical Engineering at San Francisco State University in Fall2009/ Spring 2010. The main goal and concern in this design project was trying to make a simple application based on electrical and electronic knowledge that learned from school. It included knowledge from Circuit Design Analysis (ENGR205), Engineering Measurement (ENGR300), Microelectronic and its lab (ENGR353 & 301), Design with Microprocessor (ENGR478), Linear Signal System Analysis (ENGR305). Our first main purpose was to make a portable wireless temperature control sensor and display the temperature output approximately only for usage in the car and for camping within 40 feet distance, but we improved our project by adding some features which can even control the temperature by users so that it can be used for homes' and companies' temperature improvement at a very cheap price. Our design detected temperature, transmitted and received signals, adjusted temperature and displayed temperature.

See Pictures and Videos, please click here

Parts

The following parts is needed in order to accomplish our project:

• 1 X PICAXE-08
• 3 X PICAXE-18
• 1 X Temperature sensor Dallas DS18B20
• 1 X AM Frequency Transmitter modules (AM RT4-433.9)
• 3 X AM Frequency Receiver modules (AM HRR3-433.9ND)
• 1 X Potentiometer
• 2 X 5V fan
• 3 X 4-7 Segment Module Display.
• 1 X 4.7k Resistors
• 2 X10k Resistors

Set project design up to work

The first main idea of this project is trying to understand how to use the Microcontrollers: PICAXE-08 and PICAXE-18. We programmed them using Basic Picaxe Programming Software and used Picaxe08 in the transmitter, and Picaxe18 in the receiver. We used temperature sensor Dallas DS18B20 connected with Picaxe08 and later designed to connected AM Frequency 433.9MHz Transimitter modules (AM RT4-433.9) to transmit the analog signal of the actual room temperature. In order to control any temperature we desired, we build another similar user-friendly Transmitter modules which is connected to potentiometer and 4-7 Segment Module Display which shows the set point temperature. Two AM Frequency 433.9MHz Receiver Modules (AM HRR3-433.9ND) receive the analog signals from both transmitters which then connected with PICAXE18 which compare the temperature difference and display the temperature using the 4-7 Segment Module Display. The two Fans which is controlled by the PICAXE18 are connected together with the receiver but it will be in the box separately. When the actual room temperature is higher than the set point temperature, the cooling fan will be turn on and blown all the hot air out the box. If the set point temperature is higher than the actual room temperature, the hot fan will be turn on and blown all the hot air into the box. They both will be turned on and off in order to maintain to the set point temperature. Finally, we build a clear box to see how we control the temperature.

Schematic Design

Here are the design circuit diagrams and schematics of transmitters and receiver:

Fig 1. Wireless Temperature Transmitter

(NOTE: In this transmitter, you will need the right resistors for your microcontroller.)

Fig 2. Wireless Temperature Receiver

(NOTE: In this receiver, you will need the right microcontroller in order to be compatible with AM Receiver modules and 4-7 Segment Display Module.)

Fig 3. Wireless Temperature Set-Point Controller Device

(NOTE: Potentiometer is needed to create a desired temperature. In here, this can run in the range of 32 to 300 degree Fahrenheit)

Fig 4. Wireless Temperature Control Receiver

(NOTE: You will need two BJTs and two diodes, each set for each fan.)

Actual Design

Fig 5. Wireless Transmitter

Fig 6. Wireless Set Point Control Transmitter

Fig 7. Wireless Receiver

Fig 8. Wireless Temperature Control Receiver

Background

There is a moderate temperature changes in San Francisco, and we want to know what the real temperature outside our car when we is driving. We took advantages of our idea and built a wireless temperature sensing device so that we can bring this device wherever we want, but this project is good for the companies (IBM, CISCO, etc.) which use lots of computer for networking and programming and for some households which need heater or cooling water system. They might want to know the temperature of the room where computers are and how to maintain to a certain temperature. Our design can help them see and adjust the temperature to what they would like to be.

Design Consideration

We compared the three microcontrollers MSP430, ATMEGA16 and PICAXE 08 which is best to use for our project. MSP430 is very expensive and powerful microcontroller but it has already built in temperature sensing. Therefore, we cannot use it for our design. ATMEL is another powerful microcontroller but it uses assembly language and is pricey. For Picaxe, it is very low-cost microcontroller and just powerful enough to use for our project design which use C Programming. We planned to use Thermoelectric in our receiver, but there is no where slots to put for it. When we were designing this design, we also thought about the product's cost as we wanted to build it with the maximum of $50. Check the attachment for more detail on price the device will cost.

We tried to use Thermoelectric in our receiver, but it needed more than 5V and it required a heat sink in order to get cold air and we will need two thermoelectric. So, we plan to use Amplifier LM471 again to boost up the voltage supply to other components but it require a minimum of 12 V in order to produce 10V out of it.We tried to make the design as portable as we could.

Product Result

Wireless Transmitter detect the room temperature and transmit digital signal. Wireless Set Point Control Transmitter transmit the desired temperature signal. Wireless Control Receiver receive both of the signal and compare them. If the room temperature is higher than the Desired Temperature, the Cold Fan will be turned ON. If the room temperature is lower than the Desired Temperature, the Hot Fan will be ON until the receiver equalize the two temperature difference. If the two temperatures are the same, both Fans will be OFF.

Flow Diagram

Fig 9. Design Flow Chart Diagram (Hardware)

In this hardware flow chart diagram, both of the transmitter transmit signal which receiver then detect and compare the differences which will later make either of the Fan ON depends on which signal is larger than the other.

Fig 10. Design Flow Chart Diagram of the Control Receiver (Software)

This shows how the software works in the control receiver. The receiver will start to receive transmitter's signal after it started to turn ON. "Valid" means the transmitter will show the accurate number within the range. If the transmitter's temperature signal is not received which can be either the transmitter is OFF or the result is out of the range, the receiver will wait for the signal and then forcing the signal to be received and then go to next step. If both signals from both transmitter and set point control transmitter is received, then started to compare the difference creating the fans to turn ON/OFF. Whichever the fan is ON (which means the receiver got signal and process its duty), the LED will blink and display the temperature and go back to the loop until the receiver got to the equilibrium which means maintaining the temperature that we desired.

Control System Diagram

Fig 11. Temperature Control System Block Diagram

According to the Block Diagram, the input will be the actual room temperature. The differences in between the temperature from the transmitter's temperature sensor and desired temperature of set point transmitter will go to the control receiver which later compare the result and show the output temperature signal in the receiver display.

Result in Video

Please enjoy our following video demonstration of our entire design to see how it worked by clicking it.

Discussion/Conclusion

The results are very good, and the codes work fine. It met all the requirements. It is portable; it can transmit and receive temperature signal at least the range of 40 feet distance. It can control the temperature wirelessly and manually. The limitation in this project is using only 5V to drive all devices. However, if we use 5V input voltage from battery instead of using DC power supply source into wireless temperature control receiver, the analog signals obtaining from wireless temperature control receiver got slowly which made the device more inaccurate and unstable. There might also have some frequency distortion which creates lots of noise in the control receiver while operating with the Fans. We also figured it out that lots of power is loss whichever the fan is ON and when we checked the current on the fan, it is almost the same as the total current that came out from the battery to supply all component and let less current flow through the AM receiver modules. Then the voltage will be drawn from the battery to support for the receiver modules to get more signal which make the total voltage reduce in the battery. Therefore, there is a huge amount of power consumption in the fan.

Fig 12. Waveform from the battery in the control receiver

When we use the DC power supply, the receiver device works extremely fast and very sensitive in getting signal. The waveform just only showed in a straight line with less noise. It is because it has constant voltage and current supply enough to work for all the components in the control receiver and it is very stable.

However, there are numerous possible ways to solve this problem:

Add a capacitor between input voltage source and the control receiver circuit to remove the noise so the frequency go 'clean' and get the analog signals smoothly.

Input a higher current source with 5V maximum power source to pull up both receiver modules in control receiver circuit since both two fans on control receiver would drain out all current from the circuit so the the device would be unstable.

In order to do further improvement on the project's performance for the future, we could use a following method as well:

Since we are using 5V for each device, we may use voltage step-up (Boost) converter to drive a lower input voltage into a higher output voltage. For example, A 1.2 V input AA battery and output voltage is 5V. If we can use that converter, we can add the thermocouple (also known as Peltier) to rise the temperature in the control receiver which is the heating system (e.g. heater) and cold down the temperature with a cold fan which will make our design into a cooling system design for home use (e.g., a small solar refrigerator or portable cooler for outdoor activities, or air condition). Finally, we may make our design stronger and more sensitive response on the temperature controller, may use Solar Cells as input voltage to make our design using green energy and may use a PWM (Pulse Wide Modulation) to set up a duty cycle to control the speed of fans as well. We may change the speed by changing to angular velocity of fans.