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If it simulates OK I would expect it to work as long as the layout is reasonable and the parts you use are the same as you simulated. You do need to be very careful with Cout and Cin which must be simulated with the correct esr values. The inductor must be simulated with the correct internal series resistance and must be rated for the peak current (check the data sheet to see how to work this out.)

This is a reasonably fast switcher and won't be very forgiving, some of the older designs from National Semiconductor (now part of TI) in their 'simple switcher' range worked at much lower frequencies and you might get away with a worse layout.

The reason that you really need a scope is that one of the most common ways that switchers malfunction is to pulse for  a short time, then stop, then start again and this can result in very large ripple currents and bad ripple on the supply but a DMM won't see it. Just to make life interesting some switchers deliberately work in pulse skipping mode at low powers.

I wouldn't quite give up if you are really keen - try a much neater breadboard layout with a slower switcher or if you want to practice soldering try an "air" layout (ie DIL chip in a socket on its back with the parts soldered to the leads directly. Put the Cin and Cout and L on first so they get the really short leads. It's a bit of an art but can be effective.

The picture was pulled from the web - it seems that most people don't call it air wiring. Try googling "dead bug wiring"

MK

Thanks MK,

    Since we don't have single caps and resistors with the right values, I think dead bug wiring might be a bit difficult and our switcher is 400kHz I think.  I guess we'll try to do our best and see what happens.  I'll post some more results or questions after we play around with it a bit. 

So, after soldering a perfboard together instead of a breadboard, we expected to have better results.  After getting literally noise on the output again, we decided that the chip had been blown somehow.  We then replaced the regulator chip and it gave an output as expected.  Peculiar enough however, the regulator stopped working at 9.11V input.  The expected input range was from 7-18V and although we are not using the designed components, dropping out at 9.11V is pretty interesting.  Any thoughts?  If the input is turned off and reset to lower than 9.11 it starts to regulate again.  I realize the 9.11 is just a design coincidence at this point

There are too many unknows for me to tell you what's wrong. It could be that the inductor you are using is saturating and the chip is shutting down due to excessive current. Have you worked through all the TI design stuff using the values of the parts you have. What are the specs. for the inductor you are using ?

MK

Help on taking Height Measurements using Arduino(Amendment)

Am focusing on improving the efficiency in health care delivery in rural Kenya. Most of the Health facilities in the rural parts are understaffed considering the huge number of patients that they have to serve on a daily basis.Most time and effort is wasted to undertaking simple measurements and doing data entry for the same piece of information for each patient. This wastes precious time that the health practitioner would have used in assisting another patient. I intend to solve the Height Measurement problem for now for which the patient can stand in front of a given stand with a mounted arduino which picks their measurements.The measurements are then to be sent via sms to a remote location(Doctors computer)

I hope my explanation is now clear

You need to explain more - low cost is mercury thermometer and a 2m ruler with that slider thingy that rests on your head. How does adding electronics help ? (I'm not saying that it doesn't, just that you need to describe the system a lot better for anyone to be able to advise about how to build it.)

MK

Michael,
I have re-edited my original post so that its now more clear

Thanks for the additional info. It's usually better just to add another post rather than change the content of an earlier one because this makes the thread very hard to follow.

As to height measurement - the problem with devices like this is that for them to be any use they need to integrate well within the complete environment in which they are used. This normally starts with a lot of study about what it must do and how it might be used. A classic ruler and slider system with button operated readout might work, or do you need a non contact fully automatic system. there will be huge cost differences. My first thought would be that it would be much more effective to train someone to do the basic measuring and drop the electronics. You won't get rid of the operator because the text message from the height sensor has to be associated with the patient so for each height measured you need  a manual data entry.

If you want to know more about the zillions of such devices already in production then Google for "digital stadiometer" (which seem sto be what American medical types call them.

When you know what you want to do and have  a good idea of how much it must cost and where it might be made it will be possible to design  a suitable height sensor.

MK

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