Taking stock

First task of the day is to take stock in the components bin.

My 200-in-1 electronics kit has a few possibly useful bits

• 4k:4k transformer
• 900:8 transformer
• Quad nand
• Dual JK Flip-flop
• 7 seg LED
• 2 NPN
• 2 PNP
• level meter analogue
• 9v controlled relay - controls 24V DC @ 10A or 12A @ 120V AC or 10A @ 220V DC

Microcontrollers

• AT Mega 16L - 0633J
• AT Mega 8515L - 0633
• 5 x AT TINY13 - datasheet
• STK500 AVR programmer
• NXP LPC11U24
• NXP LPC1768
• mbed breakout board (unpopulated)

Sensors

• LIS3LV02DQ Breakout - 3 axis sensor
• MPU-6050 3 axis & gyro sensor
• Samsung E700 camera with breakout
• HMC5883L - Triple Axis Magnetometer Breakout
• LV Max Sonar EZ1
• 5 x LM35 precision temp sensor
• 20 x 3mm photo transistors NPN
• 2 x minature microphones

ICs

• SN7415N 4-16 decoder / multiplexer - datasheet
• 4 x L293D push pull four channel driver for motors - datasheet
• 4n25 - optocoupler

Output devices

• Nokia 6100 LCD colour breakout
• 2 x TEC1 - 12709 peltier
• 12V solenoid
• 50ish superbright white LEDs
• 9 x 3mm red LEDs
• CIRRUS CS225/STD 6g MICRO SERVO

Discrete bits

• 4x BC547B - NPN transistor
• 2x BC548B - NPN transistor
• 1x BC549C transistor
• 2k trim pot
• 2 x 5v zener diode
• TIP127 linear switching darlington PNP transistor
• Less than 50 100nF caps (43 i think)
• 1x 50v 4.7 uF electrolytic cap
• plenty of resistors, descriptions to follow

End of Week One

At college today. Wrote a project spec and some other documentation.

Spent session two re-reading "Serial Port Complete" - Jan Axelson

This evening I read the MODSERIAL code and other serial libraries on http://mbed.org/

Found sources on ebay for MAX232 TTL/RS232 converters in case I need them, including RS232<>USB - although looking at the Atlas-Scientific page, they output 0-5v rather than +- 12v so I won't need a convertor

Did a cursory search for funding opportunities for Urban Sustainable Development projects - which is what this project to be the first step towards a full blown urban renewal project through hydroponic growing, using renewable energy sources to run HIDs when the sun don't shine, preferably a water mill.

Read deeper into Reverse Osmosis water purification techniques. Although not strictly part of the specification, RO water is preferred to raw tap water and also facilitates the use of rain / river / waste domestic water in a hydroponic system. Also by passing spent water through an RO unit it can be released safely into the environment which might be more convenient than re-using it as an input. Especially good for funding applications: a farm that produces drinking water as well as food from sea / river water or at least one that outputs waste water that is cleaner than it arrived. The RO most suitable to the starter operation is the M500P-UV which is £259 and can produce 189 litres per day, and consumable filters per year of £29.95 + £54.95 + £24.95 = £109.85

Subsequently read on and discovered that if you source your RO from the tap, lots of water >50% is not filtered at all and discharged to wherever your "waste" pipe goes, along with any precipitate. So it's better for filtering a source such as a stream or sea water but not already potable water.

My Lucky Day

Ordered the flow meter from RS, in fact, I got two.

And I ordered the peristaltic pumps from cpc.farnell for £82.62 sigh

I also ordered the three regular pumps which came to £17.64

I went all in and ordered the sensors too: conductivity £142.944 inc VAT and pH £91.50 inc VAT

A total of: £334.70 for which I worked 54 hours.

Project Week 1

I had given the project some thought but to get a concrete idea I created a block diagram design.

We had covered flow sensors in last year's sensor section. The I/O units would be gravity fed valves. The idea being that the valve opens and the the fluid runs until sufficient has been detected by the flow meter.
Upon researching the valves I discovered that gravity fed valves are the not the normal method. The simplest devices use the pressure of the fluid to open the diaphragm, such as this one from Adafruit and only £6. Valves that open with 0 pressure are called latched valves or zero pressure valves and are slightly more expensive, starting at about £25. Here's a selection of all kinds.

The second issue is that the ultrasonic flow meters I knew about are £187 each which is prohibitively expensive when I need at least 6 of them. So I considered using the same flow meter for each input.

This is a possible configuration. It does rely on the flow meter being sensitive.
I found one for 0.5-15 l/m at RS; it uses a rotary mechanism.

The next option I considered is one without a flow meter but instead uses timed delivery. This has been the stalwart of liquid delivery systems.

For accuracy I investigated peristalic pumps which seem a reasonable compromise at about £30

Before I make any decisions I need to estimate the actual volumes of fluid for each input because I anticipate needing a range of accuracy /control for each input rather than homogenous.

Ok I need something like 10ml of feed per 10 litres of water for both Solutions A and B. The Adafruit pump does 100 mL/min so 6 seconds is 10 mL. Of course I could pre-dilute it so if I did it 50/50 that 12 seconds is the same 10mL concentration but I'd have to mix 20 Litres of output.

So, in conclusion, I need three peristalic pumps to add solution and pH fixer. The water input pump, output pump and also the recycler pump can be the 9L/min pump and use a "cheap" flow meter.

This leaves me with the following block diagram: