Monday 9 January 2012

Engineering DIY

I think its time for a brief interlude from wild ramblings of my checkered past with some light entertainment. Well it will be entertaining for those who have either fish tanks or like elctrickery. So unless you are into reef keeping I suggest you skip this one. As some of you know, I have a few fish tanks, and one of those is a marine reef tank. These tanks are a bit of a balancing act when it comes to maintenance. 

Firstly, they are expensive, eye wateringly expensive. The rock is called 'live rock' because it is shipped from the sea from the other side of the world, where people put lumps of rock into the sea, wait a year and then ship it round the world, so when you put it in your tank it has all the beneficial bacteria and critters that make a reef tank possible. So how much is it? Well about £10 to £12 a kilogramme. My small reef tank has 10 Kg!! Large reefs can easily have more than 100Kg. The cheapest, smallest corals are £10, a decent specimen usually around £50 and a particularly rare species, (in the trade, not the wild), would be closer to £100 or more... The fish are similarly expensive. The equipment also costs a small fortune, and you need a lot of it, lots of lights, pumps, protein skimmer, cooling fans, heaters, sump tanks, refugiums, calcium reactors, powerheads and the list goes on.. 

The final kick in the wallet is the water. Forget using tap water or even expensive mineral water. These tanks require that you have pure water from a reverse osmosis filter which you then mix with a specialist salt. This means there are no traces of Nitrate, chlorine, chloromine, fluoride, bacteria, gunk, plasters, tissues, small dogs, phosphate or copper from the water pipes, and I'm talking levels in the region of parts per million, which will at the very least cause a massive algae outbreak in your tank. At the worst you could kill all your fish and corals.

So why do I put up with all this hassle, well take a look..



With high power lights just a few centimetres from the surface of the water and several submerged pumps the temperature of the water can rise from a stable 27°C to close to 30°C, not good. So there are fans above the lights to cool them, this also increases the evaporation rate of the tank which causes the salinity level to fluctuate which is death to corals. My own tanks salinity will fluctuate between 1.025 and 1.027 over the course of a week despite me trying to remember to add RO water to top up the evaporated water. This means I notice the water level has dropped and I chuck in half a litre of water, which causes a quick change in salinity, not good either. So I was thinking about this problem last week and decided that there must be a way of making a system to automatically add water when the level drops.

I thought about a simple gravity-syphon method, but there would be no direct way of controlling the amount added so I would need an active monitoring system. A quick brain storming session and I had several ideas on paper before choosing a system based on a switch. A sensor would detect the drop in level and activate a pump, adding water. Once the level rose back to the required level, the pump would stop. I was going to use an Infra-red LED and sensor and use the light refraction through water to block the sensor, until the level drops and the sensor would then register the beam. But a quick experiment showed that the LED's were unreliable due to meniscus effects, water beading and salt deposits. I had a dig around my odds and sods box to see what I had and came up with these quick sketches.




The only thing I didn't have available were a pair of float switches, the rest consisted of a brand new, small geared pump, a PWM motor speed controller, some resistors, LED's, a 6v DC SPDT relay, (left over from a rocket ignition system!), a rocker switch, 6v Dc transformer plug, solid core wire, jack plugs, vero board and a project box. Cue a couple of hours of frustration as I tried to transfer the prototype circuit fom a bread board to the vero board as I couldn't understand why I kept short circuiting and blowing LED's. After many LED's and a lot of shouting I realised that the vice grip I was using to hold the board while soldering, had a metal grip and was shorting the copper strips.. Doh!

The power lead, switches and pump are connected to the box via three jack plugs. The first switch will detect a fall in water level and turn on the pump, once the level rises, the switch opens and the relay turns off the pump. Now should the first switch fail, the pump could flood the tank, my room, the floor, the ceiling downstairs..... So a second switch is in place above the water level that will turn off the pump just above the limit of the first float switch. This only activates should the first switch fail, acting as a failsafe. The two LED's indicates that the system is on, and when the pump is running.

Here are the prototype and finished circuits, although the finished circuit now has two red LED's on wires rather than attached directly to the board. The final picture shows everything ready to be assembled. Just need to print some fancy labels, drill some holes for the LED's, wires ect, and it's done. Doesn't look too shabby so far, just waiting on some small diodes and a 555 timer from EBay to couple the PWM speed control circuit to the relay circuit to allow fine tuning of the pump speed. This will allow me to control how fast RO water is added to the tank. A quick test showed that the flow rate at the lowest pump rate was around 500ml an hour. A bit too fast, might have to see about either finding a new pump or restrict the flow a bit, but I will see once the system is ready to install.


Now I could have bought a commercial auto top-up system for £65 to £120 and be done with it, but I get a real buzz from designing and building my own solutions. My system works, and once finished would look just as professional, so I see no point spending so much. If I had to buy everything new, then it would have cost me around £35, but since I had everything bar the float switches it has cost me a grand total of £11. I am waiting on some diodes and capacitors to couple the PWM speed controller to the relay circuit and then I can finish it. I will of course post an update once it is complete with a demonstration video.

I'm a bad man...

So Movemeber finished.. Yet my tash lived on.. Then sometime between 6pm December the 8th and 6am December the 9th it disappeared.... In reality it was so itchy and irritated I had to shave it and could bare the pain and annoyance no more. Removing it was a major task, my moustache hair was so coarse that cutting it felt like wire. I do miss it, and would have liked to keep it. 

I should also tell you that my idea that length of facial hair correlates directly to the frequency of being ID'd in the supermarket was correct. The very first time I bought booze after shaving, I was asked for ID, and almost everytime since.

In other news I am growing mushrooms. Not magic ones nor the cheesy fungus found in the depths of John Mc'Cririck unspeakable places, but nice posh ones. I found them in a 'grow your own mushrooms' box, wrapped up in colourful paper from Aerospace Girlfriend on Crimbo day. Now when your girl buys you mushrooms for Christmas you know she is up to something. What that something is, I have no idea but one thing is for sure, it involves fungus.
RIP tash. 1/11/2011 - 8/12/2011