Author Topic: EEVblog #776 - World's Smallest Digital Dosimeter  (Read 50845 times)

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Offline dmg

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Re: EEVblog #776 - World's Smallest Digital Dosimeter
« Reply #25 on: August 06, 2015, 11:36:10 am »
Oh... resin this is most complicated thing!
I will try to explain.

My design is based on the ultra-low leakage on HV side.
For this i tested many-many different components on different manufacture and select that diodes and capacitors witch have low leakage. It should be understood very clearly. It means replace component on HV with analogs are not allowed in most cases.

About resin... The decrease in current consumption I was so successful that mosisture level in atmosphere is now be critical to current consumption.
In high moisture level it be high current consumption and battery discharging is faster. I do not like it, although in most cases it is not critical.

[...]


I was kind of expecting this, thankfully all the components in the HV section are easily available in exact part number, so no problems there. That HV power supply design is a masterpiece. I also have an ultrasound cleaner, but is it OK to clean the board with the SBM-10 installed or do I have to clean it before installation? I'm concerned about vacuum seals potentially cracking due to vibration. I'm no expert on HV/humidity barrier coatings but there are people in my company who are, I'm gonna ask them to see what can be done.

Thanks again
 

Offline AccountRemovedPerUsersRequest

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Re: EEVblog #776 - World's Smallest Digital Dosimeter
« Reply #26 on: August 06, 2015, 11:42:52 am »
Its compiled by RAD studio XE6 with JCL, noting else!

You dont need make anything, in this week i added language selector to this software.

That is very good - and the only thing I was going to do anyway.

Axel.
 


Offline Rubi

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Re: EEVblog #776 - World's Smallest Digital Dosimeter
« Reply #28 on: August 06, 2015, 11:58:10 am »
Hi Shodan!

I recommend use Seeedstudio, because it have better "Annular Ring" PCB limitations.

First thank you very much for this great project!

Seeedstudio is also great, esp. when you want to build more than one unit, but I recently prefer oshpark because of the default golden coating , at seed this would cost an extra 20$.

On another great russian project i built recently I had to use dirty pcbs which were extremly cheap and also very good quality but it nearly took two months to get to me.
http://dirtypcbs.com/view.php?share=6586&accesskey=cad38a0e9484b06ec39b33055847b133

Cheers
Michael



 

Offline VK3DRB

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Re: EEVblog #776 - World's Smallest Digital Dosimeter
« Reply #29 on: August 08, 2015, 08:59:13 am »
What the country of Japan needs is a tool to detect radioactive trace elements in their food. Invent that and you will become very wealthy. In the meantime, many Japanese are buying foreign fish because they do not trust the stuff from local waters.
« Last Edit: August 08, 2015, 12:52:00 pm by VK3DRB »
 

Offline Skibane

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Re: EEVblog #776 - World's Smallest Digital Dosimeter
« Reply #30 on: August 09, 2015, 04:14:09 am »
"World's Smallest"?

Not sure about that...



 

Offline drago

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Re: EEVblog #776 - World's Smallest Digital Dosimeter
« Reply #31 on: August 09, 2015, 01:29:28 pm »
Awsome project!
I like the clean design especially the high voltage converter but also other features:
 • user interface
 • Nokia display
 • USB ESD protection
 • cute vibration motor
 • digital design

Thanks for sharing this as an open source.
 

Online Kleinstein

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Re: EEVblog #776 - World's Smallest Digital Dosimeter
« Reply #32 on: August 10, 2015, 08:27:28 am »
Food testing is much more complicated. The radiation levels are much lower, so one needs quite heavy shielding.
Normaly they also use only gamma radiation, but a energy seperated cintilation detecor. The expensive part is the detector (special crystal and photomultiplier tube). The electronik can be small and cheap - though in small quatities it has a price. Even than it takes hours to get a usefull reading, unless  the radiation levels are way to high.
 

Offline dmg

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Re: EEVblog #776 - World's Smallest Digital Dosimeter
« Reply #33 on: August 10, 2015, 02:11:28 pm »
Hi again, I just received the main components order but I'll take about a month to get everything else from china. I can't find a datasheet for the screen, do you have one? Could you at least tell me the main dimensions (width, length and thickness) of the screen so I can model it in 3D for the case design?

I live in a part of Spain with relatively high levels of natural radiation. Right where I live it's about 15 uR/h just in gamma radiation according to available maps, but in the mountains nearby it can go up to 30 uR/h. I plan on taking this to mountain trips and monitor the radiation.

EDIT: also, do you have a source for the button plastic keys? I've seen in your blog that you used calculator keys in previous designs but now all your cases have the same black buttons. I can't find them on ebay.
« Last Edit: August 10, 2015, 02:27:16 pm by dmg »
 

Offline dmg

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Re: EEVblog #776 - World's Smallest Digital Dosimeter
« Reply #34 on: August 10, 2015, 03:01:00 pm »
Thanks, I'll get that exact calculator if possible.

Right where I live the soil is basically sand and river sediments but the mountains nearby are mostly made of granite and that's why radiation is higher than average. I hope this device can detect the extra radition.

Besides that, I think that the only potentially highly contaminated area in Spain is near a small southern town where a yankee plane accidentally dropped 4 atomic bombs in 1966 and the explosives in one of them detonated spreading plutonium over a large area. Thankfully it wasn't a nuclear explosion. They cleaned most of the stuff but as far as I know there are places that are still contaminated. I might visit that place one day.
 

Offline SNGLinks

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Re: EEVblog #776 - World's Smallest Digital Dosimeter
« Reply #35 on: August 10, 2015, 11:52:00 pm »
Thanks, I'll get that exact calculator if possible.

Right where I live the soil is basically sand and river sediments but the mountains nearby are mostly made of granite and that's why radiation is higher than average. I hope this device can detect the extra radition.

Besides that, I think that the only potentially highly contaminated area in Spain is near a small southern town where a yankee plane accidentally dropped 4 atomic bombs in 1966 and the explosives in one of them detonated spreading plutonium over a large area. Thankfully it wasn't a nuclear explosion. They cleaned most of the stuff but as far as I know there are places that are still contaminated. I might visit that place one day.

That's near Vera Playa where I go on holiday every year!
 

Offline JackM

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Re: EEVblog #776 - World's Smallest Digital Dosimeter
« Reply #36 on: August 11, 2015, 10:00:37 pm »
Total cost ordering in 1's is about 60€. If anyone is interested I can share a cart for digikey/mouser with everything you need in exact quantity (once you stockpile about 8 large boxes full of leftover SMD's you start seeing the value of ordering just two damn 0603 resitors even if that's more expensive than ordering 25 or 50 as you did when your room had more space)

I am interested in sharing a cart. I am located in Canada however, which might make things more difficult. Let me know!
 

Offline TheElectricChicken

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Re: EEVblog #776 - World's Smallest Digital Dosimeter
« Reply #37 on: August 12, 2015, 12:41:11 pm »
because it need complicated milling like this and this. It make by the hands with Dremel and "file" in first prototype. Last versions fully doing on CNC machine.

I want to help with this important project. I want to make for myself. I can print 3D, I can Draw 3D. I design for 3D printing. Can you post measurements ? I can draw and post STL file for 3D printing for free. I want to help.
 

Offline JackM

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Re: EEVblog #776 - World's Smallest Digital Dosimeter
« Reply #38 on: August 12, 2015, 11:33:24 pm »
shodan, I've got a question about the chosen values for the resistor network configuration on the buck converter.

Based on the schematic, you've chosen to go with the 4-resistor configuration detailed in the TPS62736 datasheet. It's basically two resistor voltage dividers for the VOUT_SET and the VIN_OK_SET pins that determine the output voltage and set the acceptable VIN threshold to control the VIN_OK output indicator logic pin.

In the TPS62736 datasheet it recommends that the sum of the two resistors in each divider be 13 Mohm. In your schematic you've got a 7.5 Mohm and a 5.1 Mohm resistor for the VIN_OK_SET divider. I was wondering why you chose the 7.5 Mohm instead of an 8 Mohm resistor? Is it because you wanted a slightly lower (2.989V) VIN_OK threshold? I would have figured you'd go for 3.1V as a threshold, but maybe there is something I'm missing here.

Also, for the resistor divider on the VOUT_SET pin, the sum of the two branches (R16 + R17||R20) is no where close to 13 Mohm, it's more like 5.5 Mohm. Why is this? Is it to achieve a very slightly higher input quiescent current?
 

Offline dmg

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Re: EEVblog #776 - World's Smallest Digital Dosimeter
« Reply #39 on: August 14, 2015, 10:31:30 am »
Hi, I have just received the two SBM-10 I ordered. I am concerned because they make a rattling noise when you move them, like they have something loose inside. Is this normal or did I get two broken geiger tubes?
 

Offline Rubi

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Re: EEVblog #776 - World's Smallest Digital Dosimeter
« Reply #40 on: August 14, 2015, 01:08:17 pm »
Hi

Mine also rattles, hopefully this is by design.

Cheers
Michael
 

Offline dmg

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Re: EEVblog #776 - World's Smallest Digital Dosimeter
« Reply #41 on: August 15, 2015, 04:47:08 pm »
The seller has told me that some SBM-10 were manufactured with fixed getters, while others have unfixed getters and thus they rattle. Is that a possible explanation?

They don't rattle the same way, one of the tubes sounds like if it had a completelly loose ball inside that can move in any direction while the other sounds like it has a ball attached to some flexible structure/spring. I'm not sure about what's the deal in here, I don't know how the internal structure/components of this tubes would look like. On the other hand considering how small they are I find them quite difficult to break...
 

Offline dmg

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Re: EEVblog #776 - World's Smallest Digital Dosimeter
« Reply #42 on: August 15, 2015, 05:21:21 pm »
I won't get all the parts until late august so I won't be able to test the tubes until then... and ebay buyer protection will have already expired by then, that's why I'm investigating if this rattling is important or not. Apparently rattling SBM-20's are sometimes sensitive to movement and that would be unacceptable for me:
https://mightyohm.com/forum/viewtopic.php?f=15&t=3388

This is exactly what the seller has told me about the fixed/unfixed getters:
Quote
Some manufacturers made tubes with fixed getter, but few manufacturers made is unfixed. it is absolutely normal.

In vacuum tubes (triodes, pentodes, etc) the getter is typically a ring of metal  that they heat after the tube is sealed (they call that flashing) so it sputters a coating of metal that adsorbs residual gases and helps to keep the vacuum. As far as I know geiger tubes aren't in a vacuum and don't require a getter. (https://ru.wikipedia.org/wiki/%D0%93%D0%B5%D1%82%D1%82%D0%B5%D1%80_%28%D0%B3%D0%B0%D0%B7%D0%BE%D0%BF%D0%BE%D0%B3%D0%BB%D0%BE%D1%82%D0%B8%D1%82%D0%B5%D0%BB%D1%8C%29)
 

Offline dmg

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Re: EEVblog #776 - World's Smallest Digital Dosimeter
« Reply #43 on: August 25, 2015, 10:46:05 am »
Today I've received the PCB's and cases and everything fits well. The only components I'm still missing are the screens (on their way but quite delayed because of some "chinese military manouvers"), the vibration motors and some diodes that were out of stock and got sent yesterday so they'll arrive tomorrow. I would have assembled the PCB today if I had the missing diodes... I'm travelling tomorrow and I'll be out of town until september so I'll have to wait.

I have 6 spare PCB's. Let me know if anyone wants one.

 

Offline Rubi

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Re: EEVblog #776 - World's Smallest Digital Dosimeter
« Reply #44 on: August 29, 2015, 05:22:01 pm »
Hi

I ordered the 8.06 pcb, does the 8.02 firmware work with this board ?

Is it possible to buy one or two cases from you ?
I am not the best in cutting plastic,...

Cheers
Rubi
 

Offline Rubi

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Re: EEVblog #776 - World's Smallest Digital Dosimeter
« Reply #45 on: August 29, 2015, 05:23:58 pm »

I have 6 spare PCB's. Let me know if anyone wants one.


I could also give some away within the european region.

Cheers
Rubi
 

Offline dmg

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Re: EEVblog #776 - World's Smallest Digital Dosimeter
« Reply #46 on: August 30, 2015, 07:38:49 am »
What do you mean by thermal barrier is missing in some pads? Does it mean that you wanted pads to connect like the left image and they connect like the right one? [img]http://i.stack.imgur.com/MkZdx.png[\img]

I still haven't received the screens but now at least they have  left china.

BTW I have 6 cases and I only need 2. I don't think I'll get the machining right the first time and I'll sacrifice one for testing the plastic with my cnc's tools to get the correct speed and feedrate. In the best case scenario I'll get 4 machined cases so 2 spares if anyone wants one.
 

Offline osiixy

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Re: EEVblog #776 - World's Smallest Digital Dosimeter
« Reply #47 on: August 30, 2015, 10:06:48 am »
At the first blink it was not obvious what that image tried to show, so probably the info below would be helpful to others also.

thermal relief
Since copper is an efficient heat sink, connections to a large region of copper would be very difficult to solder - the copper heat sink prevents you from adequately heating the connection. To fix this, small cutouts are made around each such connection to create a thermal barrier, so that heat applied to the connection stays at the connection. Such a set of cutouts, and the copper bridges that remain, is called a “thermal”. Thermals come in many patterns, which allows the designer to ensure adequate electrical connectivity and/or manufacturability.


Pins with no connection, three types of thermals, and no thermal.



Thermal pads can be seen in several locations on this Printed circuit board (PCB), in particular, the bottom pad of the three vertical pads in the top left corner.



Sources:
« Last Edit: August 30, 2015, 01:02:23 pm by osiixy »
 

Offline dmg

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Re: EEVblog #776 - World's Smallest Digital Dosimeter
« Reply #48 on: August 31, 2015, 06:32:21 pm »
Well, I've almost assembled one ultramicron. I still haven't installed the geiger tube because I've run out of isopropyl alcohol so I can't properly clean the PCB yet, I'll buy some tomorrow and install the geiger after cleanup.

Here are some pictures:
Part way through assembly:

After reflow and fixing some minor shorts. Note the flux residue.(yes, I've reflowed the motor but I think these are reflowable and if not... well... YOLO):

Charging the battery (led not visible due to flash):


As you see I've done a little mod to include a connector for the battery. It's an SMD connector hacked to somewhat fit in there. I've checked and there should still be enough clearance with the case. I've also checked that the geiger can still be assembled and fit in the case this way.

I have uploaded the DFU bootloader succesfully and then loaded the firmware via DFU. No problems there. The micron is detected as a virtual com port but I have issues with the USB geiger program. It doesn't detect the micron automatically (I've assigned the micron to COM2) and this is how the program looks like in my computer (Win 7 64bit, windows classic theme, 1920x1080 screen resolution):


Any clue?

Also, after assembly, programming and powe up I've checked the voltage at the tube terminal and my crappy multimeter tells me it's 200V when it should be 400. Probably the multimeter is loading the supply too much to keep the voltage up... what do you think? I'll check with a real high-z meter at work one of these days.

« Last Edit: August 31, 2015, 07:11:12 pm by dmg »
 

Offline dmg

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Re: EEVblog #776 - World's Smallest Digital Dosimeter
« Reply #49 on: August 31, 2015, 07:33:59 pm »
Ouch, I've turned it off right now, I hope I haven't fried the mosfets. I checked the voltage at the HV cap and my crapmeter says 317 V. Anyway I still have materials to build another one in case this one doesn't work or I've fried something.

I'll have to wait for the screens as I still haven't received them. Hopefully they'll be here this week....

edit: Yes, I run on medium or big fonts. But don't worry, after you dowload the logs it becomes usable.
« Last Edit: August 31, 2015, 07:36:41 pm by dmg »
 


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