Surf 1.2 PI power supply advice requested please

[Magnette]

Good evening all,

I am anewbie to this forum and also pretty much a novice at building my first detector. I wondered if anybody may be able to advise me about the Surf 1.2 PI that I am currently building. I have read in several different places that this kit can be run on a range of voltages. With this in mind, I have built up my kit carefullyand finally got to the powering up stage. I have seen people using various different batteries and power packs, so though I would give a standard 9v battery a go. Switch on and... nothing. Do I need to be supplying this kit with around 12v to get it to work? As I say, I have different peoples views that a variety of voltages work with this kit and hoped it would work with this battery to try and save a little weight on the machine. Any advice would be appreciated.

Thanks, Magnette.

[Tepco]

Using 9V battery is highly not recommended. Not only due to limited capacity and cost, but also due to relatively high internal resistance. Surf will tolerate wide voltage range, consumption is about 50-60mA, 9-10 rechargeable AA or AAA cells (will work with 8 is probably best decision, you need proper charging circuit for NiMH or polly cells, if you can find old fashion NiCd cells you can charge them with simple resistor)


If you can get regulated and current limited bench PSU for first test would be nice, to avoid holly smoke, batteries don't provide current limiting. Do not use old PC SMPS (noise) and wall-plug adapters (possible large voltage variation between open and load condition). If you need to improvise, add 7812 regulator with two capacitors to larger wall-plug with large enough (15-18V) output voltage.


Be careful to avoid reverse polarity and overvoltage, over 15v can damage components.

[Magnette]

Thanks for your advice Tepco, I do have about 12 NiMH AA batteries that werer bought for my Minelab when I had it a few months back, and are no longer being used. I also have the wall charger for them, so charging is not a problem there. I did wonder about the 9v battery, as I hadn't seen anybody else use them in the various youtube videos that I have watched. Also, is it possible to get the piezo sounder the wrong way round? just a thought. The coil that i have made is a 14" mono loop, which is made from a single core of spare CAT5 cable. I have given it 15 turns which has given a resistance of 1.6ohms, which I figured was quite within range. Is there anything else that I should perhaps look for also, or just tyr one thing at a time?

Many thanks, Magnette

[Tepco]

One thing at a time, as usual. Powering something from 12V battery is usually 10.8 to 13.8V. Surf will work from 9V but coil peak current will be smaller and as battery discharges, somewhat below8V, internal circuitry will lose regulation, not a good idea.


Coil issue is most important in all this, due to number of reasons. First, not coil resistance but inductance is important, target around 300uH, anything between 250 and 400 will work. Keeping low resistance is recommended, below say 2R, if you use too thin wire and get 5-6R, this will affect performance. Limiting peak current available for given fixed TX time, it will waste energy on ohmic resistance, instead of storing energy in magnetic field, not good idea again. Some detectors are designed with high resistance coils, even resistors added etc, but not this one, keep resistance at some reasonable level, be careful about inductance.


Most important about coil is “speed”, or minimal sampling delay achievable with given design. Dictated by inductance, parasitic capacitance (separation between conductors), shield material, if used, coil wire material (wire or Litz) etc. Lot of this is discussed on forum before. Ordinary bundled wire coil is simplest to made, not too fast but will work (limited by parasitic capacitance, windings too close). Some other designs, using teflon, or PVC insulated wire, or specially shaped coils (basket coils) are better. I devised here one interesting design, using flat spiral speaker wire coil, easy to make and very fast. It was intended for completely different use, fact that it can be successfully used for Surf is just a side effect. Also with different coils, shielding problems can be different, and you may not be able to utilize full speed advantage without some detector parts modification.


I used CAT coil just for large coils, like 70x70cm, never tested it on Surf. With large coils and large detectors, intended to search deep and large stuff, speed is not an issue, but for Surf, intended to find small objects, jewelery etc (fast decaying targets) it is very important. I don't think CAT coil will be good for this, it can work, detect metal etc, but due to large parasitic capacitance, twisted pairs with shield etc, it will probably completely suck. To get some benchmark, Surf is originally designed for around 20 or so uS sampling delay,(to prevent salt water interference) 30uS or more can be considered slow for this,(about what you will get with CAT), 15 uS can be considered fast, 10uS or below is really good, but hard to achieve. Large coils use 50uS or more. Hope this was informative to some degree.

[Magnette]

Thanks once again Tepco for your advice. To be fair, a a novice, some bit are probably a bit above me at the moment, but Ibguess that I will learn in time. Tha CAT5 coil that I have wound is not a pair of twisted wires, but a single core wire taken from a pair of twisted wire, so just one core.

I hve seen the speaker cable coil on the Adrianandgenese website, but don't recall the wire gauge for the cable. Perhaps you could advise me of the best gauge to use?

Many thanks, Magnette

[Magnette]

Apologies for the spelling mistakes. I tend to never look at the screen when typing before hitting return!!

[Waikiki_Sweep]

I can recommend to use three 18650 Li-Ion 3.7V rechargeable batteries.
They will give you 2000 mA/hour or more at full load.

At full charge it gives 4.2 Volts each or 3 X 4.2 = 12.6 V

They contains much more energy and significantly lighter in weight then any other rechargeable batteries. Otherwise why every electronic device in the world using Li-Ion or Li-Poly batteries now.

You can buy 18650 cells for $1-2 each on eBay, you need $2-3 for holders for 5 cells. Charger for 2 cells costs near $3. Holder for 3 cells $1.29

Also there are very good 18650 cells you will find if disassemble any broken battery from notebook, laptop, netbook computer.

Than you will have free and literally unlimited source of power for your PI detector. 500 charges for every cell.

[Magnette]

Thanks for the tip Waikiki. I will certainly have a look into that. I have a couple of scrapper laptops kicking around work, so will attack the batteries there first.

Regards, Magnette

[Magnette]

Hiya chaps, I wonder if I may call upon your knowledge a little further. As a temporary power supply, I connected the surf up to a power supply from a car battery charger, which gives a constant supply of 11.7v. On turning the surf on, I got an extremely quiet constant tone from the piezo sounder. This was not affected by moving either of the control knobs. The only ways of getting any tone any louder from the piezo were to move the coil virtually on top of the piezo sounder, or swap the sounder and coil connections around on the board. This gave a full loudness tone to the piezo sounder, but still could not be controlled or detect anything. Any ideas of what may be wrong (apart from a rookie like me building it!) would be appreciated.

Many thanks, Magnette

[Waikiki_Sweep]

Good news that coil and TX probably works. Bad news that you have assembled something wrong or some parts are broken.

Check presence of supply voltage + 5V and - 5V on the board with multimeter first.

Check it on LM358 -5V ( leg 4 ) and +5V ( leg 8 ) to the ground of the board ( contact "-" of power supply ).

See the picture:

[Magnette]

Thanks for the advice Waikiki.

I will check this a little later when I get a chance and report back.

Regards, Magnette

[Waikiki_Sweep]

Also you have to set zero volts to ground on leg "6" of preamplifier NE5534 with using "Offset" trimpot. Preamplifier will not work without correct offset adjustment.

[Magnette]

Hi Waikiki,

Thanks for pointing out about setting the offset to zero. I had done this already, so I guess at least it shows that it is working to a point. I haven'y had a chance you to make the other checks that you suggest, but I intend to have a look a little later on today and then report back. Its a bit frustrating when you build something and then hit a bit of a wall like this! I suspect that it is something simple though. As an electrician, rather than an electronic engineer, I can only hope that I have assmebled it correctly. I appreciate that capacitors are polarity sensitive and was careful to ensure that they were fitted the correct way round. I also sorted all of the other components out so that I could be sure that I was fitingthe correct bit in the right place. The only bit that I was a bit unsure of though, was the little red square components, which I believe are a type of capacitor. There was nothing on these to indicate which way round to fit them. Both legs were the same length, nothing appeared offset in any way and there was no markings to suggest they went one way or the other. With this in mind, I figured that it did not matter which way round they went. Another concern was if I may have set some of the resistors a little low in the board and possibly have cooked them with the soldering iron. Finally, I wasn't very convinced by the molex connectors either. Initially, I didn't get any noise from the board at all. On inspection, the connectors didn't seem to be making very good contact. After pushing them a bit harder into the connector block, this was when I started to get a very faint signal from the piezo sounder and reaction fom the coil. I am considering soldering the all of the wires straight onto the connector pins on the board to eliminate this problem, starting a wire at a time incase this is the cause of my problem.

I will let you know in a while the results of your suggestion.

many thanks, Magnette.

[Magnette]

Hi again Waikiki,

I have checked the voltages at the legs on your suggested microchip and and I am getting +5v and -5v as you have indicated, so I guess at least that bit is working. Any further suggestions that you may have would be greatly appreciated.

Thanks, Magnette

[Waikiki_Sweep]

Check if you have inserted ICs correctly. For example CD4066 and CD4093 (MC14093) stay face to face.
Bad soldering is a sickness of any DIY kits. Get a big magnifying glass and try to find places where unexpected contacts on PCB may occurs. Clean PCB between IC legs. Look for bad contacts where solder was cold. Re-solder such places. Use flux when soldering. Remove flux remainings with isopropil.

First, use 10k resistor to check if you have a sound and oscillator working:





Also you can check impulses in some key points: