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Last update : 2020/09/05

Build the Flashmeter / Lightmeter for smartphone and tablet

Do not panic, there is no need for knowledge in electronics and computer to make and build this cell
measuring light. Read this tutorial, I give all the information to do it.

If you have any questions or problems during the implementation, they should be asked in the forum, in the
"Questions / Answers" section, in the bottom of the forum (in the left menu of the website, there is a link to the forum).
And the answers will be useful to other people. I do not answer questions by email.

To make the Flash meter / Light meter, you must buy electronic components. I provide a PDF (components list.pdf),
a list of components to buy, with all references (in the ZIP file 'Flasmeter", left menu of the site, "Download" link).
The file "component list.pdf" is composed of several columns: Designation (component name) Boutique (the seller's website),
reference of the component on the seller, the quantity that you order, the price and a comment column.
Caution ! If you want to order electronic components away from my seller E44 ,
read the comment column in the PDF file.

Some electronic components can be purchased on sites sales electronic components online on the Internet.
I chose the E44 website ( ) to give you all references and price.
This online website selling electronic components,do postage delivery throughout France for 5 Euros (shipping costs).
They can also make deliveries in Europe and also in the world, but for Europe and world, you will send them an email
with the list of electronic components that you want to buy, for know the amount of shipping costs to your destination.
To find the electronic components on the E44 website, simply put the reference that I stated in the PDF file,
in the "search" field at the top right of the site E44 .
I chose the E44 website because I often order from them, the prices are often very low and shipping costs are not expensive.

It will also buy some components on Ebay, same as the Arduino pro mini, Bluetooth module,
FDTI module for programming the Arduino pro mini, the PIR module for the diffusor.
In the PDF file "Component list.pdf" I separate the electronic components to buy from E44,
and components to buy on Ebay. For components to buy on Ebay, I can not give you links directly (or vendor names)
as prices change often (often lower). I give you the name of the component to search in the field Ebay search.
To find the correct component on Ebay, you simply specify the name that I wrote in the column "Designation" in the Ebay search.
Do not forget to search including vendors abroad (world search for best price).
By default, Ebay only offers sellers in your country (therefore prices are much more expensive).
For very low prices, choose vendors in China, vendors Chinese deliver worldwide.
Another recommendation for your search on Ebay, do a ranking by "Price + Shipping least expensive." Ebay
payments are made by Paypal, so, you need to create a PayPal account, if you do not. I buy regularly in China by Ebay,
and I've never had a problem with delivery, sellers are very serious. Delivery times are long (between 3 and 5 weeks),
but the prices are really interesting.
There are several models of FTDI and PIR module.
On Photo01, I'll show you the right components to buy, and those that do not buy.
- For the PIR module, you must purchase a module with an elongated shape and a small diffuser.
- For FDTI module, it must be 6 pins and with above indications: GND, CTS, VCC, TX RX and then DTR.
And if you see indications GRN and BLK, that are very well. This will allow you to put quickly the module FTDI
in the right direction on, for programming the Arduino Pro Mini.

Photo02, the material that I used to make the flashmeter and lightmeter cell for smartphone and tablet.
- A small drill to make holes in the box enclosure.
- A drill with a mini disc (mini drill, this is not mandatory, but will help to cut the legs
of the box enclosure, or for cutting the hole of the switch).
- A cutter (which will replace the mini drill to cut the legs of the box for example).
- A flat pliers.
- A wire cutter (to cut the legs of the components after welding).
- And finally, most importantly, a soldering iron with a fine tip (30 watts maximum power) and also the tin ...

For soldering components, it is necessary to use a printed circuit (PCB).
This project is aimed at people who do not have the knowledge and equipment to make a printed circuit board (PCB).
To optimize and minimize the circuit board, I opted to make a double sided PCB with metallized holes.
Many holes are metallized under the connectors, and are used to pass from the first side to the second side.
So, even if you have the equipment to manufacture PCB , you can not do PCB with metallized holes and you can not make
contact between the two sides. That is why, I propose to order the PCB to a specialized company and you send it.
I do not think hundreds of people ask me a PCB, and the post being next to my home, I therefore propose to serve,
for this a order PCB by 5, which allows a PCB for 14,91 Euros.
For one unit, the price is 80 Euros, because the specialized company invoice a minimum of 10 cm * 10cm.

If you are interested to make this project, send me an email (my email address is written down in
the left menu of the website, in the buttom).
I'll give you the link to make a Paypal payment and I will send to you the PCB by postal with tracking.
Paypal gives you proof of payment and a guarantee if you have any doubt about my seriousness.
The sending letter with tracking, provides a guarantee that the PCB has been posted and you have received
(it is a guarantee for me).
Depending on your country, Paypal takes a fee for the transaction
(from 3.4% in France and 5.2% in other country + 0.25 Euros).
Here is the cost price of the printed circuit board (I rounded up a few pennies).
For France: PCB 15 Euros + 1.51 Euros Paypal fee + Shipping 1.51 Euros = 17.50 Euros (rounded)
For Europe: PCB 15 Euros + Paypal fee 2.52 Euros + Shipping 4,75 Euros = 21.50 Euros (rounded)
For the rest of the world: PCB 15 Euros + 1.50 Euros Paypal fee + Shipping 6.60 Euros = 23.50 Euros (rounded)

To solder the components on the PCB, you need a soldering iron (30 Watts max and fine tip) .
You can buy one from E44 for 5 Euros
(placing your order for only once, for reduce shipping cost).
Think also of tin to solder (3 Euros for 50 grams).

Now let's get serious, the build !

Photo03, the layout diagram of the components, it is useful, because it has both the name of the component (eg C2).
So remember to consult the Photo03, when you have a question for soldering a component.
This will allow you to be sure of its name, but also the direction to weld.

Photo04, all components necessary for producing the cell flash meter / meter.
From top to bottom and left to right: AAA battery holder, the Arduino pro mini, resistors,
the box. Then below, the Bluetooth module, the converter 3/5 Volts, the jack, connectors.
And finally, the PIR module, switch, transistor, the PCB, the photodiode SFH203
(missing Photodiode BPW21R on the photo), capacitors and the FTDI module.

Photo05, the first thing to be welded, it is the connectors on the Arduino Pro Mini.
Photo05(1), the Arduino pro mini comes with unwelded male connectors.
We will cutting, two female connectors of 12 pins and a male connector 6 pins
to replace the angled male connector supplied with the Arduino, same as the Photo05(2).
Hint: for solder the connectors on the Arduino pro mini correctly,
use the females connectors that you have cut, as in Photo05(3).
Now, cut a female connector of 3 pins and a male connector of 3 pins for the converter
3 to 5 volts, as the Photo05(4).

Solder the male connector of 3 pins, on the converter 3 to 5 Volts, as the Photo06(1).
Now we will weld the first components on the printed circuit : the two photodiodes.
On the Photo06(2), I made small red circles to show you that the photodiodes are keyed.
The keyed is used to indicate the correct direction.
Photodiode BPW21R (yellow = P1) has a keyed, with a shaped tip, to weld the photodiode,
in exactly the same direction as the Photo06(2) .
The photodiode SFH203 (white transparent = P2) , has a flat keyed (flat side),
we can also identify the keyed through the shorter leg.
CAUTION ! Look well Photo06(3), the two photodiodes are welded upside down on the PCB.
They are not welded on the front side, where there is the white markings on the printed circuit,
but on the other side.
These are the only two components to be welded to the back side,
all the other components are welded on the front face of the printed circuit.
Photo06(4), we will weld the two female connectors of 12 pins (A1 and A2)
which was previously cut (Photo05).

Tips: place the Arduino pro mini on both connectors of 12 pins to weld it correctly, as in Photo07(1).
Thus, you will be on, they are correctly weld.
NB: You notice the photodiode on the other side of the PCB ...
Photo07(2), we will solder the female jack that is used to sync flash (J1).
Photo07(3), the female jack welded.
NB: you will remember to remove the nut on the thread of the female jack for
insert the flashmeter in the box, the red arrow on the Photo07(3).
Photo07(4), the first two capacitor of 100nF welded (100 nano farads).
Their names on the diagram of implentation are C2 and C5.
These capacitors have no meaning.
The color of these capacitors may be yellow, blue, orange, this does not matter.
You just reads the values ??written above, and weld the two capacitors with "100n" written on it.

Photo08(1), weld the 10nF capacitor (C1), this capacitor is marked "10n".
This capacitor has no meaning.
Now we will solder the last two capacitors.
These two capacitors are different, they do not have a rectangular shape but a round shape.
CAUTION ! These two capacitors have a sense that we must respect.
For the side that goes to ground (or GND), locate the white or black strip.
This white or black strip will always be on the side of the shorter leg.
These capacitors may be brown colors, blue, orange, black, ...
It is not the color that matters, but the written value above (1 uF or 22 uF).
On Photo08(2), the capacitor of 1uF (micro Farad).
You must bend the legs at 90 degrees, with white or black strip on the right side as on the Photo08(2).
Photo08(3), the 1uF capacitor (C3) welded, with this white or black strip on the right side (red circle).
Photo08(4) , the capacitor of 22uF (C4) with the legs bended, but the strip is on the left
(the inverse of the other capacitor).

Photo09(1), the two capacitors of 1uF and 22uF welded.
CAUTION ! you noticed that strips are not the same side.
You noticed that capacitor 22uF (blue for me) is higher than the other capacitor.
This is normal, the circuit is so small, that there is not much place.

We will now weld the 4 resistors (R1, R2, R3 and R4), Photo09(2) and Photo09(3).
If you purchased the little bundle of resistance in E44, like me,
there are 6 resistors in the package.
We need 4 resistors.
The resistors have colored rings for identification.
The resistors values is in Ko or Mo ( Kilo Ohms or Mega Ohms) .
- R1=100Ko (100 Kilo Ohms) and its colors are: Brown, black, black, orange and finally green.
- R2=9.5Mo (9.5 Mega Ohms) and its colors are: White, White, White, yellow and green.
- R3=10Ko and colors are: Brown, black, black, red and finally green.
- R4=1Ko and its colors are: Brown, black, black, brown and finally green.
Watch Photo09(3), if you buy the same resistors like me at E44.
If, against you buy your resistors by another vendor, you may have other colors:
- For R1, you must have five colored rings because it takes a 100Ko precision resistor of
0.5% or 0.1 %, the colors will therefore Brown, black, black, orange, and either green or purple.
- For R2, If you have chosen a resistor of 4.7 Mo, the colors will be
Yellow, purple, green, and gold ring. In all cases, the last two colors are green and gold.
- For R3, the colors will be Brown, Black, orange and finally a gold ring.
- For R4, the colors will be Brown, Black, red and finally a gold ring.
The gold ring indicates that you have purchased conventional resistors, with a 5% accuracy.

Now, we'll move on to the serious stuff ...
Photo09 (4), weld the first resistor R1 of 100K 0.5% or 0.1% (Brown, black, black, orange and green).
I made a small red circle to show you that you need to bend the leg of the resistance
very near, because there is not much place in the box.

Photo10(1), weld the BF256 transistor (T1). With the Red circle, I show that tin is pull up
through the hole of the transistor during soldering.
This means that I put a little too much tin, but it's not serious.
At least the transistor will not move !
Photo10(2), we will bend the pins of the Bluetooth module with flat pliers.
Photo10(3), the 4 pins of the Bluetooth module bent at 90 degrees with a small space.
Photo10(4), the Bluetooth module is soldered onto the printed circuit (BT).

Photo11(1), weld the 3 pins connector that had been cut for the 3/5 Volts converter module,
and solder it as shown by the red arrow (DC).
Photo11(2), cut a female connector of 2 pins and welding it (1 and 2 in the layout diagram Photo03).
This connector of 2 pins is used to connect the switch.
Photo11(3), there remains a small space between the two connectors for to the resistor R3
(Brown, black, black, red and green).
Photo11(4), solder the resistor R2 (White, white, white, yellow and green).

Photo12(1), finally weld the last 1Ko resistor R4 (Brown, black, black, brown and green).
CAUTION ! For this last resistor, I placed the leg towards the edges of the printed circuit
to prevent it from touching the Arduino Pro Mini, when it is in place.
Photo12(2), one can place the conversion module 3/5 volts on the 3 pins connector.
Photo12(3), you should be cut two connectors of one pin and solder it.
this two connectors are used to make contact with the support of AAA battery.

Here, the electronic part is finished !
Turning now to the box !

Photo12(4), we see with red arrows, the columns that we will have to cut and remove.
Photo13(1), the result the box has no columns inside.
Photo13(2), all the holes to do in the box.
Photo13(3), the printed circuit going inside the box with a little force.
To correctly slide the PCB in the box, first put the jack into their hole,
then force on the PCB, for between inside the bottom of the box.
Photo13(4), we see the bottom of the box with the two photodiodes.

Before placing the Arduino pro mini in the box, it must be programmed.
We will use the FTDI module:
- Connect the FTDI module to the Arduino, as the Photo14(1).
If you have information GRN and BLK on your FTDI module, you will find the same information on the
Arduino pro mini.
Otherwise, it will take a good look at the other indications: DTR, RX, TX, PWR, CTS and GND to set
FTDI module in the right direction.
Following a comment on the forum, I said, only one FDTI module is neccessary.
On the Photo14 (1), we see my two FDTI modules, this is to show you the different indications.
We must therefore buy only one FDTI module.
It must be modify the FDTI connector, because by default, it have a male connector.
It must a female connector, for connect to the Arduino Pro Mini.
As it will remain a small piece of the female connector 40-pin, it may be used.
It must be unsoldering the male connector, present by default, for solder the female connector,
or making a female / female adapter.
- Connect the USB cable to your computer.
Windows will detect the FTDI module and install the driver.
- In the ZIP file Flashmeter, I provided a program called "Download Program in Flashmeter.exe"
XXXX is the version of the ZIP file.
Launch the program "Download Program in Flashmeter.exe" and click the button, to program the
Arduino pro mini automatically.

Here's the Arduino Pro Mini is ready, it is programmed.
You can use the FTDI module, if there are updates to the program the Arduino Pro Mini.
This may allow for improvements and new developments.

You can place the Arduino pro mini module to its location in the box.
Look good sense like the Photo14(2).

We will now make a few small cuts on support for AAA battery.
This will allow to place it precisely in the box.
Photo14(3) and Photo14(4), small red circles,show to you, the cuts to the
Support AAA battery.
The two arrows of the Photo14(3) indicates, the two pin, to bend.
This will allow to make contact, same as the Photo15(3).

Photo15(1), cut the box, to dimension of the switch.
Solder two wires on the switch and on a male connector of 2 pins.
Photo15(2), the switch is connected to the printed circuit.
Photo15(3), we can see the contact between the two pins welded on the PCB,
and the AAA battery holder.
I have not welded AAA battery holder with the PCB, it is to be able to
remove the entire assembly, if necessary.
There is still one important thing to do, it is to remove the small button "RESET"
on the Arduino pro mini, because it will interfere with the closing of the box.
It also may trigger unwanted reset of the Arduino.
this micro switch can be opened with a knife or screwdriver.
Photo15(4), switch "RESET" removed from the Arduino.

If you would like to put a jack male, to provide a support for a smartphone or tablet,
Make a hole and fix the jack in the box as the photo16(1).
Photo16(2) the jack fixed inside the box.
The only use of this jack, is used it for fixation, it is connected to anything.
Photo16(3), cut the columns of the box cover.
And finally, we must drill a small hole in the lid of the box.
This hole will permit to let the light of the power of the Arduino LED.
Through this hole, you can know if the mounting is power on or not.

Here, the build is completely finished and ready to be used.
It takes about 4 hours to build this flashmeter / lightmeter cell.
Tip: take your time, make sure that you do it right to successfully perform it the first time.
If you have any questions or problems, I will answer you in the site's forum.

Photo17(1) and photo17(2), I used a female jack to make me a necklace.
So during a photo shoot, I can have my cell around the neck.

Photo17(3), the cell attached to a Samsung Galaxy ACE.

Photo17(4), a first test with a small measurement in incident light, and
with illumination by a halogen desk lamp.

Photo18, the cap used in reflected light. This cap is 20 mm and fixed on
the light sensor. To use this cap, remove the hemispherical diffuser.

I hope I have provided enough information to make by yourself the "Flashmeter / Lightmeter".
If you have any problems, if you have any questions, you can ask it in the forum.
I do not answer questions by email, only questions in the forum.
Sorry for my poor english, if you have correction, don't hesitate to post it in the forum,
after I will perform a correction.

All photos and texts are subject to copyright and distribution rights.
Reproduction in whole or in part, photographs and texts, without permission, is strictly prohibited.
Any commercial use of this arrangement is subject to intellectual property rights.
So thank you not to reproduce or distribute internet images and texts of this DIY.
Implementation and use of this DIY is allowed in a personal or school environment.

Copyright 2014 ThierryD -
First update 08/01/2014
Last update 16/02/2014
Reproduction prohibited

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