# 3. Assembly and Reflow ## 99 decimal counter: Assembly Assembly Time! Now that you have deposited solder paste on your circuit, all that is left to do is place your components and reflow the solder on the board. {% hint style="info" %} We have a component staging print out that you can use to layout all your parts in the correct orientation before placing them on your board: {% endhint %} {% file src="/files/fmwBmW9NTU3OFa4hUwUT" %} ### Surface mount components The circuit requires the following components that have been included with the pulse generator kit: * NE555 IC × 1 * Blue LED × 1 * 100kΩ resistors × 1 * 47kΩ resistors × 1 * 330Ω resistors × 1 * 0.1µF capacitor × 1 * 1MΩ trimming potentiometer × 1 * 1µF capacitor × 1 * Wire connector × 5
Carefully place your components onto the corresponding pads, as shown in the board layout below.
{% hint style="success" %} Use the tweezers included with V-One to place components precisely. {% endhint %} Do not smear the solder paste when placing components. Once they are placed, press down gently so the components rest evenly on the pads.
Both the LED and the electrolytic capacitors have a polarity. Remember to double-check that they are placed in the correct orientation before you solder them to the board. When in doubt, reference the circuit schematic shown above.

This potentiometer has 3 separate contacts shown above. Keep these points in mind when placing the component on the corresponding pads.

The solid paint stripe indicates this component's negative terminal

Once all of the surface mount device (SMD) components are placed, proceed to the **HEAT** step. {% hint style="info" %} Even though diodes are typically marked where the cathode is, there are, of course, exceptions to this rule. Because of this, it is very important to carefully review the datasheet of every diode/LED that you plan to use in your future designs. {% endhint %} ### Reflow Now that all of the surface mount components are placed, the circuit is ready to be reflow soldered. 1. From the **Start** menu, select the **HEAT** workflow. 2. Click the **REFLOW** tile. 3. Select the solder paste you're using, based on the lot name printed on the cartridge label. 4. Click **REFLOW** to start the process.
{% hint style="danger" %} V-One gets hot while reflowing. Do not touch! Do not leave unattended while heating! {% endhint %} When the heating cycle finishes, V-One will start glowing blue. This means the soldered PCB is safe to remove. ### The result Plug in a 5V power supply or connect the pulse generator board and watch your circuit come alive. If everything is working, the LED will be lit and blinking at a steady rate, and you can control the blinking speed by adjusting the potentiometer. You should also be able to measure oscillation from the middle signal connector on the output side of the board. The top connector should be a steady 5V, the middle signal connector should change in rhythm with the flashing LED, and the bottom connector is ground. If you have an oscilloscope, you should also be able to measure the square wave. First, connect the probe to the oscilloscope and then to the circuit's ground and signal output. Adjust the probe's compensation for a sharp waveform. Next, adjust the Volts/Div and Time/Div settings until the square wave is clearly visible and stable on the grid. Finally, use the grid, the oscilloscope's built-in measurement tools, or cursors to find the peak-to-peak voltage, period, frequency, and duty cycle of the signal.
Congratulations! You have completed the pulse generator circuit board. That concludes the tutorial. If you ran into any hiccups along the way, let us know at . As a reminder, this circuit is part of a set of circuits designed to work together in a series. You’ll need to complete the voltage regulator circuit or have a steady 5V power supply as well as complete the 99 decimal counter circuit to operate this circuit.
Cover image
Voltage Regulator Project/files/n9rDk2Np1MckOAjJSY1o/pages/TfV1FdG80YRbQegs5fok
99 Decimal Counter Project/files/nmTDZvEDto14rvWtO0J9/pages/EBVd2zlsyA4okCvegAeT
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