Idea 1:
- Doesn't allow a variable frequency
- Rather simplistic design for a second year project
- Use of solenoid adds an important safety feature
- Gas canisters are much too large for a portable device
- Does not employ a way to display the frequency
- Servo would still allow gas to flow if power was cut
- Does allow for a varied frequency
- Duty can also be altered unlike 555
- Allows for a way for frequency to be displayed
- Although cheap, it is the most expensive option
- Takes up a rather large and limited PCB space in a handheld device
Idea 3:
- Variable frequency can be achieved
- No precise measurement or display of selected frequency
- Frequency can be easily calculated
- Components are inexpensive
- The gas canisters/chargers are rather expensive, however are perfect for a portable application
Development of chosen idea:
For our final idea, we have decided to use push to make switches as our input to alter the frequency. Also, it will be the input to control gas flow. For the control we are going to use an 8 pin PIC. This will allow us to cut down on board space as it has the same layout as a 555 IC, also the 8 pin is a much cheaper option than its larger counterparts. This will keep our costs down an in-line with the 555 and Mosfet options. For the output we are going to source a normally closed gas solenoid, as this has an included safety feature, in addition to being easily controlled via PIC, unlike its servo alternative. For the display of frequency, we are going for 2 options, our first being an LCD display, which will change according to the user input of frequency. Since this adds a great deal of complexity to our design in terms of PCB size allocation and programming. We have decided on a back up of a more simpler LED which will vary in brightness if the frequency is either Low, Medium or High. Since this is a portable application, designs for a voltage regulator for the PIC chip, along with indicators for battery level will also have to be designed and added.
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