In this first part the unsoldered components are through-hole components, which means that component pins are passing through the PCB. The tool used to unsolder those components is a standard unsolder stand (shown in the SMD unsolder part below) which allows to unsolder component by selecting a heating temperature (in this case 400°C) and by connecting the hot point of the tool with the solder.

The first method used to unsolder those components, consists in a quick heat of all the pins of the component in order to melt the solder and slowly take it out of the PCB with smooth strength. This method has an inconvenient: if the component is taken out in order to be checked, the strength used to take out the component, could damage the component if not controlled.

The second method used is based on the use of an air unsolder gun. The extremity of the gun is heated with a chosen temperature. The body of the pump has a trigger allowing the activation of an inside orientated stream of air which aspirates the solder out of the component pin after heating it with the extremity. This method is a lot cleaner than the first one if well done: It takes out all the soldering and the component can easily be taken out with no strength.

In order to use it properly, the hole at the extremity has to be put in contact with the solder with a planar surface and move around in order to heat the solder uniformly. Then when the inside stream of air is activated the tool must be fixed in a position and the component heated during about 5 seconds.

The first method is efficient for low number of component pins If there are more than 3 pins the first pin solder gets cold before the last pin solder has been heated. When increasing the number of component pins it's necessary to use the air gun in order to obtain a cleaner job.

The components soldered here are SMD components. Those are small component mounted on the surface of the PCB. The difference with through-hole components is that it's not necessary to drill the PCB to solder them and that their size allow a higher integration density of component on PCB.

The methods used to unsolder SMD's components here is the same as the first method described before, by quickly heating the pads of the component with the unsolder tool and taking it out with a little strength on the side.

One of the problems of those components while trying to unsolder them is their fragility. It is important to know that the pads on which they are soldered are stocked into the PCB and that it's necessary to leave the pads on the board if the aim is to check the component. In this case the pads have to be heated long enough so that the components can be taken out but not too long to avoid component overheat. As their thermal resistivity is low the SMD's component can't be heated more than 5 seconds at a temperature of 400°C.

The hot air unsolder method is another way to unsolder components on a PCB really useful case of a high number of pins components. The first step of that method is to select the heating temperature and the air pressure as shown on the picture below:

The second step is to heat the pads of the component with the air stream until the component pad solder melts. Then the component can be taken out of the board with the clamp . The method is really useful and quick in the case of numerous pin components but it has to be done with uniformity what can be complicated because of the movement of the air stream needed to unsolder all the pins at the same time. Nevertheless as the output size of the hot air tool is large in front of the size of the components the risk of burning the component is higher than with the standard tool.

In this part a microscope is used in order to have a good vision of the position of the components. The microscope has to be set up first: the focus has to be made over the pads of the components to be soldered. Two tools are used to realize the solder: a clamp and a solder station.

To solder a SMD resistor the first step is to put a little amount of solder on both pads of the resistor footprint paying attention to the amount of solder: If there is too much on, then one side of the resistor will be higher than the other one and the thermal dissipation will decrease because their will not be a board contact any more. Once this amount of solder is put, the second step is to drop the resistor at its exact position thanks to the clamp. When the resistor is dropped it is necessary to keep it into position with the clamp and heat both sides in order to stick it on the board thanks to the little amount of solder previously put onto the pads. Finally both sides of the resistor can be soldered with a bigger amount of solder: enough to embrace the all conductive part of the resistor but not too much to keep the resistivity of the solder low enough in front of the value of the resistor itself and to avoid the antenna effect if the circuit is used under RF conditions.

The method is the same as the one described above for resistor except that a transistor has 3 pads and taking into account that the first pad to solder is the lonely one which fixes the component position and make easier the soldering of the 2 other pads

An industrial method consist on passing a tin wave down the board with the components placed. This method is really efficient in the case of through-hole components soldering when all through-hole components stay on the same side of the board and no SMD components have to be soldered on the TOP layer.

Another industrial method consists on putting the PCB in an oven during a short time, which provides an air flow on each side of the PCB. this method is really efficient to sold any types of components, at the opposite of the previous method this one can be used to solder SMD on both side of the board under the condition that the temperature is chosen in consequence.

This industrial method consist on passing a high power infra red laser over the component to be soldered, the difference with the convection reflow is the ability to select a small heated area but the time used to solder all the components is longer. This method has different efficiency depending on the material used, the temperature and therefore the power of the IR to use depends on the component package.

The PCB on which elements are going to be identified is as follows:

On the PCB we can notice via which indicates that the board combines both SMD and through-hole components. As different via sizes are present on the board we can imagine that vias are used for testing signals on the board or to drive signals from one side of the board to the other side, if there was no other way to route the nets because of the components placement.

On the picture below which is a zoom from the last picture, we can see a series of SMD pads for a component size between 0604 and 1210.

This third picture shows a 208 square component probably corresponding to a micro-controller QFP footprint as the one shown below

On the last picture below, we can see different footprint pads. The first top-left one is a SOIC 20 component footprint corresponding to a 20 pin integrated circuit. The second top-right footprint corresponds to the biggest SMD 2 pads standard footprint: a 2512 footprint for passive component.The last footprint corresponds to a SOT 23 footprint most of the time used for SMD transistors

This project is a timer which allows to provide to a passive load (for example a light) the sector voltage and current during a selected time. The product built has to provide two options to the customer: the possibility to modify the time during which the power is provided to the load and the possibility to activate the power supplying. Moreover the product has to be designed such as the sector power coming in comes out to the load during the selected time.

The two main parts of this project which are the mechanical design, and the electronic design are presented here as two separated processes. In fact those two processes are not independent. The first step of the project has been to design a suitable circuit and simulate it in order to check the theoretical suitability of the circuit and at the same time begin the design of the package with the idea of the user needs, then to define the needs in term of electrical components knowing which components were going to be used the package designing can be improve in order to fit both the user needs as well as size and place occupied by the components. This last step defines the position of the components on the PCB. Once both the mechanical design and then the PCB's component placement done, it has to be checked that the PCB fits into the box and how it will be included into it. At this step the support of the PCB is designed inside the box. When all the components are placed and the mechanical design is done the product is virtually finished. Still the tools available to build the product have to be taken into account in each phase in order to be able to build it by ourselves, and one of the biggest constraints imposed by this last point are the ones imposed by the printing machine used to print the box of the product. Indeed the size of the product is limited to the biggest size of the 3D printer. The design of the box has to be done so that the printer could print it from down to top, considering, for example, that right angles are in practice complicated to print. The following diagram is a summary of the product conception process:

Knowing the steps followed during this project, the following document presents a summary of the product design by categories.

The main idea and design of the timer circuit comes from an internet design from the website 34 proyectos sencillos de electronica :

The circuit works in a really easy way, the function is based on the use of the 8 pins integrated circuit LM555 which works in this situation as a monostable circuit. To understand how the circuit is working it's necessary to see how the LM555 is made:

On the image above extracted from the data sheet of the component, we can see how the eight pins of the IC are linked inside the package. The first eight pins are the supply voltage pins, the pin number four is the reset pin working on a low level and set to the positive supply voltage to enable the timer. The pin number two is an input value of trigger compared to a voltage corresponding to the third of the positive supply voltage. The pin number three is the output of the IC and the pin number seven is a link to the discharging transistor enabled by the intern Flip Flop device of the IC. the pin number five fixes the input voltage that has to be imposed on pin number six in order to change the comportment of the circuit (by default two third of the positive supply voltage). The way the LM555 works is summed up by the following table extracted from the data sheet of the component:

So in order to use this component as a delay generator, it has to be controlled by a voltage. The trigger voltage is set as the control voltage, when its value is above the third of the positive power voltage the timer is disabled, pin three voltage is low, as pin seven voltage almost equals pin six voltage which almost equals the positive supply voltage. Considering that the capacitor has been at rest for a long time, the discharging transistor is on and the voltage of pin seven equals zero. The function of the push button of the first circuit linked to the pin number two is to change the value of the voltage on that pin. When activated, the pin number two voltage falls from five volts to zero changing the output (pin number three) values from low to high which allows the bipolar transistor 2N3904 to pull some current from the power supply through the relay turning it on, with it providing the sector power to the load and charging the capacitor C1. By then the push button has been released so the pin two voltage has increased to the power supply voltage, and we can see in the table that the next state of the output depends on the value of the pin six voltage. The capacitor C1 has not gotten enough time to charge above the threshold value imposed by the pin number five, so according to the table the circuit state remains the same as before and the capacitor C1 continues to charge until the two third of the positive power supply voltage. At that moment the output pin three falls to zero and the discharging transistor turns off. In this circuit, the time of the delay is set by the RC circuit composed by R2, R4, and C1.

The simulations are made with the software Proteus for its simple way of use and for the availability in its libraries of active components here used to press a push button during the simulation.

First the circuit is designed on a schematic sheet in Proteus and simulated to check its good functioning:

On the second image we can notice the good work of the timer part of the circuit: the yellow curve on top is the pin number two voltage of the IC, the blue curve is the pin number seven voltage, the red curve is the output pin number three voltage, the green curve is the voltage of: the capacitor and pin number six. When the push button is activated, the voltage of pin two falls and rise again just during the time the button is pressed, the voltage of pin three and seven has the same behaviour: rising even if at the beginning pin seven voltage slightly follows the raise of the capacitor voltage. When the capacitor voltage reaches the control voltage of pin five, both output and pin seven voltage falls.The simulation validate the theoretical behaviour.

Even if the behaviour is the one expected, we can notice that the decrease of the capacitor voltage is the exact opposite of its increase and lasts exactly the same time, this behaviour is due to the potentiometer R4 situated between the capacitor and the discharging transistor. The problem of that bad behaviour is that if someone uses the circuit, the next use needs to wait the fall of the capacitor voltage below the control voltage. To improve the behaviour of the circuit, a PNP discharging transistor is added between the capacitor and a smaller resistance in order to decrease the falling time of the capacitor voltage:

Now on the above simulation we can notice that the falling time has been reduced even if a small voltage is still present at the end, this behaviour does not disturb the functioning of the circuit. It has to be noticed that the base transistor voltage is the output voltage, in fact a PNP transistor needs a low level on its base in order to pull current from the voltage supplier so that when the pin three voltage falls to zero, it activates the transistor and drains the current out of the capacitor.

The simulation is made for a potentiometer value of 6kOhms to make the simulation fits onto the scope screen.

Finally we also check the relay part behaviour to ensure a good work:

On this scope screen, the yellow curve still is the pin two voltage, the blue one is the output voltage, the red one is the second transistor of the circuit collector voltage and the green one is the voltage in the load. We can easily check the good working of that part of the circuit by a look at the green curve which is on during the desired time.

In order to reduce the power consumption of the circuit, the choice is made to impose to the LM555 IC a 5V power supply. This choice impose different parameters:

- the trigger threshold is set to 1/3*5 = 1.66V

- the Control Voltage is set to 2/3*5 = 3.33V

As we also know that the time is set by the RC circuit in which the raise time is T = RC, this time represents the time for the voltage output of the RC circuit to raise from zero to 63% of the imposed input voltage which is here 5V, finally this time RC corresponds exactly to the raising time from 0 to 3.33V. If we set the maximum delay of the timer to 60s, keeping a capacitor of 100uF it imposes a maximum value of potentiometer R4 of 60/(100*10^-6) = 600kohms.

in order to reduce the falling time of the capacitor voltage to approximately 2ms and knowing that the voltage to dissipate is 3.3V, the value of the resistance to use is R=T/C=(2/100)*10^3 = 200Ohms, and in this situation, the transistor has to dissipate a current of i=C*Du/Dt=((100*3.3)/2)*10^(-3) = 160mA this kind of current is supported by a lot of transistor, a basic one is used in this circuit

this circuit is extracted from the website Sonelec :

The aim of this circuit is to provide to the timer circuit a stable 5V voltage and enough current to make the relay and the LM555 work

The functioning of this circuit is quite simple too,firstly the sector voltage is reduced, secondly the Graetz bridge is used to rectify the voltage, thirdly the capacitor filters the signal in order to obtain at the input of the L7805 5V regulator a voltage almost stable. The two other capacitors are placed in order to filter the high frequencies of the sector voltage.

To ensure a good functioning of the whole circuit, we need to know the consumption of the timer circuit, by checking in the data sheet, it can be find that:

-the relay is consuming 40mA under 5V of voltage

-the IC LM555 is consuming 6mA under 5V of voltage

-the L7805 regulator can supply a current value from 5mA to 1A with an input voltage from 8V to 25V

If well alimented by at least 8V and 6mA, the regulator can supply the 5V and 46mA needed by the timer circuit. The regulator needs at least 8V of input by choosing an input of 13V we ensure a good functioning of the component and if the current equals 6mA at the input, the power dissipation is 6*8=48mW which is way below the maximum power dissipation of the component. The transformer at the input needs to transform the 230V of the sector into 13/sqrt(2)= 9.19V and a hundred of milliampere in order to supply enough to the regulator. If so the first capacitor absorbs 90mA under 13V and a frequency of 100Hz because of the voltage rectifier, if we fix a ripple value of 100mV the value of this capacitor has to be C=I/(U*2*Pi*f)=(90/(100*2*Pi*100))*10^-3=1433uF. The two other capacitors are chosen according to the original circuit to erase the high frequencies off the regulated voltage.

In this part the circuit is simulated in order to check its good working

We can see on the simulation above that the circuit is working properly, with a small ripple of proximately 100mV and the input of the regulator which is the ripple fixed by the choice of the capacitor.

This part is a summary of all the components used in this project

Condensator C1

C1

Condensator C2

C2

Condensator C3

C3

Condensator C4

C4

Resistor R1

R1

Resistor R2

R2

Resistor R3

R3

Resistor R4

R4

Resistor R5

R5

Resistor Rd

Rd

Potentiometer Rp

Rp

Transistor Q1

Q1

Transistor Q2

Q2

Transformator T1

T1

Voltage rectifier Bridge

bridge

LED LED1

LED1

Diode D1

D1

Push button S1

S1

Timer NE555

NE555

Relay RL1

RL1

Connectors IEC (IN-OUT)

IEC

Regulator 5V-Reg

5V-Reg

The mechanical design has been realized at the same time as the simulation was realized with the Dassault System software Solidworks. The main idea followed to build the box of the product was to make it simple in order to print it properly at the end and usable so that all the user needs would be satisfied. The work is shared between two main parts, the first one is the design of the bottom of the box and the second the design of the top.

The first design of the top of the box was made to have an idea of how could the box be. It has been designed with random dimensions with the idea of the shape desired. Also the connectors between sector and circuit and between the circuit and the load were imagined to be plugged directly:

On this first design four things are important,first the three holes at the top of this part are from top to bottom : the space of the push button, the space of the potentiometer and the space for the first sector connector designed in another part. The second interesting thing is the closing system, the small hole visible through the sector connector hole is a part of it, on the bottom part of the box, and extruded part of the same size as this hole and at the same place is designed, this is the closing system of the box.

The design of the sector connectors has been made with the idea that it would be possible to solder the sector nets directly to the PCB:

Finally those connectors were forgotten replaced by IEC 320 connectors.

This second design was necessary because of the sector connector replacement. The new connectors drive the current from the sector to the circuit through a cable which changes the orientation and the place of the connectors on the box:

The place of the connector is now on the side of the box shared with the bottom part which makes the product easy to use with cables. Also the dimensions are now the dimensions of the PCB built at the same time

The last step of the design is to add the logo on it, the technique used in this case is to load an image with a bitmap extension on the surface to be extruded and to draw with the Spline Solidworks tool a sketch, following the border of the logo.Then the extrusion can be done from the sketch.

The bottom design has been done afterwards to fit with the top design and the PCB. The aim of the bottom is to hold the PCB and fit with the top to close the box properly:

On the picture above we can see the important elements of the bottom part: the closing system on the side which is the small extrusion fitting in the hole of the top and the PCB holder in blue. The grey line represents the PCB layout designed by importing the PCB into Solidworks in order to be sure that the PCB would fit into box and on its support.

Next pictures are showing the box in the Cura software environment showing the printing time of both top and bottom parts:

The software used to simulate and design the circuit is not the same as the one used to design the PCB which is Altium Designer. The first part of the PCB design is to draw again the schematic of the circuit in order to easily generate the PCB afterwards:

This circuit is the same as the one designed and simulated with Proteus. Once this circuit is generated and all the components are correctly linked to one another, the Altium's tools permit to build directly the PCB with the net link between the components information:

with the components generated with the net information, it's possible to drag those components and place them in order to fit the mechanical design.

The first version of the PCB has been designed with the idea that direct connectors were going to be used:

On this first version of the PCB we can see that the in and out connectors are placed to be used as cable soldering pads. Once the decision has been taken to use the PCB connectors the PCB has been updated:

The new version of the PCB shows the good placement of the components and the real connectors which are going to be used in the definitive version of the circuit. The dimension on the PCB is used to check the dimensions used to make the mechanical design. After this version is obtained and the mechanical design dimensions checked, the PCB is exported in order to verify the good placement of the PCB support the situation of the hole of the potentiometer and the space situation of the connectors.

After the component placement and after the good matching between the box and the PCB verification, the PCB's components can be routed:

The last step of the PCB design is to insert the logo, the name of the designer and the product name on the PCB. This can be made thanks to the logo creator script provided by Altium which is transforming any image with a bitmap extension to an image on any layer of the PCB. The name of the designer and the name of the product have been created with paint and the logo has been imported from the internet.

After the electronical, mechanical and PCB designs are done a 3D modelling of the product is possible. The first view of the 3D model is the view of the top and bottom parts of the box assembly:

On the two pictures above, we can see the match between the top and the bottom part of the box. We can also see the center of mass of both parts. The right picture shows the closing system matching between top (hole) and bottom (extrusion).

The next three images show the matching between the 3D PCB model exported from Altium and the bottom part of the box.

Those images show the good matching between the sector connectors and the bottom part of the box and also the center of mass of the PCB.

The next images give a view of the matching between the PCB and the top of the box.

We can see that the potentiometer fits into the hole at the top what allowed to modify its value, and that the connectors fit in the space.

The next views are full product views. The push button here in red is mounted on the box and then linked to the PCB with soldered cables.

The price of the whole development of this project is given in the bill of material pdf document. Considering that the price of one hour of development is 10 Euros, the total price calculated is 1,269.692 Euros.This price is calculated with the RScomponent supplier prices.

In the case that the videos should not play you can download them in the download section at the end of the page.

Here are two photos of the box printed with a 3D printer

This project has been heavy and took a lot of time because of a lack of knowledge of the different softwares used. However it has also been a great opportunity for me to discover and learnt how to work on new softwares and thus increase my knowledge in the electronic circuit development field.

During the development, there has been numerous mistakes made. At the beginning, the method was confused and I did not realize that it was really important to make a choice of component and fix it before beginning the mechanical design, and so the first version of the box wasn't even built to fit with the connectors. The second mistake has been to consider first the electronic and PCB design before the box design which, at the end, gives a product with no real fantasy in the design.

However, the objective of designing a product has been reached, the simulation and electronic designs were to me the easier part. The complicated part has been the PCB design, 3D components design with Solidworks, and to make every part fit with each other.

This project has a lot of possible improvements:

The electronic design is heavy because of the use of a transformer. This part of the design could be improved and so could be the electrical consumption by designing another supplying method. If the maximum time of the timer needs to be increased, the use of a bigger capacitor is recommended as the potentiometer already has a high value.

If the weight of the product can be reduced by redesigning the supply, so can the size of it. Reorganizing the components placement could lead to a space optimization of the PCB. Some of the footprints also have a lack of information and could be improved by adding symbols on the top layer for example.

The size of the box could be reduced by reducing the size of the PCB. Moreover the heat produced by the regulator and by the transformer is not dissipated out of the box. In order to improve the mechanical design ventilation holes could be included in the design around the hot components of the circuit. The potentiometer could also be calibrated in order to have on the box a visual information of the time selected.