RE: Building the DSO Shell 15001K Oscilloscope

jw0752 — Sat, 20 May 2017 16:40:25 GMT

Final Chapter:

One of the points of having a small Oscilloscope like this one is to make it portable. I went looking for a suitable battery pack for its 8V to 10V power needs. I also wanted the pack to be based on an easily available battery such as the AA. Unfortunately the only 9 volt configurations available had an open configuration with the batteries exposed. While this was functional it did not serve my aesthetic sense. Finally I settled on this 12 volt AA battery pack with a built in DC adapter plug and a power switch.

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At $3.50 and free shipping from China it was a no loose choice. 12 Volts, however, is too high for the Oscilloscope which has a 10 volt max limit to its power input. My first remedy to this problem was to build a small 9 volt linear DC regulator using a 7805 regulator and a 4 volt Zener. I also put a 9.5 volt Zener across the output to clamp any voltage above that level and protect the Oscilloscope. This worked very well except for the fact that the 7805 regulator was having to dump 25% of the battery power as heat. This meant that for every set of 8 batteries that I would be using two were going to be used to heat the box. Here is a schematic of the linear regulator circuit that I was using.:

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At this point I remembered that I had a bunch of the Recom R78 series devices in stock. These are switching DC to DC convertors that are great substitutes for the linear 78XX series of regulators. They, unlike the linear versions, do not waste as much power as heat. With 90% + inefficiencies one of these would be a good replacement for my linear design. I chose to use the Recom R78C9.0-1.0 which is a 9 volt 1000 mA direct convertor so I would not have to use the Zener trick on the ground lead to boost its regulated output. I will give you a link to a similar device from the Newark site. ( a 500 mA version of the 1000 mA device I am using). Unfortunately Newark doesn't stock the 9 volt device so you will have to check one of the other suppliers if you want to buy one or two of them.

http://www.newark.com/recom-power/r-78e9-0-0-5/dc-dc-converter-9v-0-5a/dp/84Y3692?ost=R-78E9.0-0.5&scope=partnumberlookahead&exaMfpn=true&anyFilterApplied=false&searchref=searchlookahead&searchView=table&iscrfnonsku=false&ddkey=http%3Aen-US%2FElement14_US%2Fw%2Fsearch

Here is a picture of the Recom R78C9.0 alone and also one of the device installed in the battery pack:

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I had a concern that a small ripple from the switching circuit might affect the oscilloscope so I put a 22 uF tantalum across the output. This was probably an undue concern as my past experience has been the the ripple on the output of these devices has been irrelevant for my applications. The power wire from the battery case was shortened so that it neatly wrapped around to the DC socket of the Oscilloscope.

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Since the power switch on the battery pack cuts power to the R78C9.0 as well as the Oscilloscope I put a recommendation on the battery pack to used its switch as the power switch and not the Oscilloscope Power switch. While the idle draw of the R78C9.0 is very small there is no sense wasting battery power. Here are a couple pictures of the completed battery pack modification.

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John

RE: Building the DSO Shell 15001K Oscilloscope

DAB — Tue, 25 Apr 2017 18:24:51 GMT

I like it.

For that price I could use them to monitor a lot of active sensors visually.

I may have to pick up a couple of these tools.

DAB

RE: Building the DSO Shell 15001K Oscilloscope

balearicdynamics — Tue, 25 Apr 2017 07:25:15 GMT

Some comparison respect the features of the BitScope mini? This device is almost cheap (about the same price of a BitScope) but autonomous. With the BitScope I should plan to add 80$-90$ for a PI or more if including it in a case to make portable. But I have also considered that in most of the cases the oscilloscope is used in some kind of lab, home lab, garage etc. where a PC is always present...

Enrico

RE: Building the DSO Shell 15001K Oscilloscope

mcb1 — Tue, 25 Apr 2017 06:16:40 GMT

Nice find.

have you tried to see what the bandwidth is ??

With a 200K bandwidth (Perhaps a bit of an exaggeration)