Logic Gates: Learn Your Logic
Congratulations on your new Logic Gates Advanced Learning Board from eLearnTronics.
On this page, we’ll walk through the steps to get this board fully soldered. You should have the following equipment:
- Soldering Iron
- Electronics Solder
- Some sort of fume extractor
- A clean heat safe work surface (ideally a soldering mat)
- Flush cutters to cut component leads
- Eye protection
If you are comfortable with your soldering technique, and you simply want to jump in, then as a reminder – follow safe soldering practices, wear eye protection, and protect your fingers from the incredibly hot soldering iron.
You’ll need to solder the components in the following order to make your life easiest (going from closest to the board to further off the board.
- Resistors
- Tact and DPDT switch
- Transistors
- LEDs
- Barrel Jack Board connector
- Attach the standoffs and machine screws
For more in-depth instructions, keep on reading.
Step 1: Resistors
You always want to solder your components starting with the components which sit closest to the board. You can follow these instructions, or you can check each component type individually. The component that will almost always sit closest to the board is the resistor.
We’ll begin by soldering the resistors. First, identify the values of your resistors.
To identify the value of a resistor, you’ll need your resistor(s) and a resistor chart which you received in your kit
You should see a color value on your resistor. Those correspond to the resistor chart card.
Identify the first color on the left. (The gold or silver band will go on the right)
Take the first 2 values (or 3, if there are 5 bands), and combine them. Then multiply by the value for the second to last band.
Now, place the individual resistors in place. The direction does not matter with resistors.
You’ll need to bend the leads where they meet the resistor, then place them in the corresponding position. Each resistor is labeled with a value.
It is important that you put the correct resistor in the correct position!
Once the resistors are placed, you can solder down one point per resistor. After that one point is tacked down, flip the board over and see if the resistor is flush. If it is not, you can reflow the solder and press the board against your table surface to get the resistor flush. Once the resistor is flush, then you can solder the other point down.
Pro Tip: Don’t place all the resistors at once. Place a few at a time, spaced apart from each other. This will keep the leads from getting in the way of one another.
Once the resistor is soldering in place, carefully trim the lead. You should hold the lead, then trim it very close to the board. You should wear eye protection, as leads can have a tendency to fly when clipped.
Take your time, and get your solder joints right. It can be challenging to fix a soldering mistake on a board with more complexity and component density, like this one.
Step 2: Switches – Tact and DPDT
You have 2 types of switches in your Logic Gates kit. Tact switches (you may know them better as Buttons, or momentary switches) and a DPDT (Double-pole Double-throw) switch, better known as a slider switch.
These will be next in your soldering of this board. For the tact switches (buttons), you’ll need to place them in the appropriate positions. The tact switches are a bit tricky to place due to their bent leads, but once they are in place, they’ll hold very well.
Begin with the tact switch. There are two of them. Once they’re placed, you can solder down one point each. Check that they are flush (they almost always will be due to the structure of the leads)
Once you’ve verified that, you can solder the other 6 points.
You will not need to trim the leads due to the already short structure of the tact switch leads.
Next, place the DPDT switch (which is the on/off switch)
You’ll place this component – the direction does not matter. Once placed, tack down one point. Check that the component is flush. If it is not, reflow that point and then use the table to flush it up.
Once the switch is flush, you can solder the other 5 points. There are no leads to clip.
Be careful with this component. Due to the metal structure, it can have a tendency to heat up quite a bit.
Step 3: Transistors
Next, you’ll solder the transistors in place. Transistors have a very specific direction that they must be placed in, but it should not be too complex to work out. Each transistor has 3 leads, and the footprint on the board matches the shape of the transistor itself.
Place each transistor following the footprint on the board. The shape of the silkscreen on the board matches the shape of the transistor.
If you place a transistor backwards, your board will not work!
Once a transistor is placed, you can solder down one point, ensure the transistor is straight (it will not sit flush with the board) and then solder the other 2 points.
Pro Tip: Start with the 4 transistors furthest in the 4 corners of the board. This will create a stable surface, so other transistors will sit flush against the table when soldering
Another tip: don’t place all the transistors at once. Place a few at a time, placed far apart on the board. This will keep the leads from getting in the way of your soldering iron.
Once all 3 points on the transistor are soldered, clip the leads carefully (hold them, then clip, so they don’t fly all over the place). Repeat for all transistors until they are all placed.
Note: Your transistors will never be perfect. The nature of the TO-93 package (that’s how we describe the shape of the component) means that it will never sit perfectly flush.
Safety: The transistor can transfer a LOT of heat from the lead to the component itself. Be careful not to touch the transistor when soldering, as it can get very hot.
Step 4: LEDs
LEDs must be placed with a very specific direction. LEDs have 2 ends on them. An Anode and a Cathode. (The anode is the positive side, the Cathode is the negative side)
If you place the LED incorrectly, it will NEVER light up.
You should place the LED appropriately. The Anode will have the longer lead. The Anode goes in the Square pad on the board.
However, the easier way to identify the correct orientation: Each LED has a flat spot on the bulb itself. Each footprint on the board has a flat spot. Ensure that the flat spots match up, and the LED will be placed correctly.
Just like our other components, place the LED, solder down one point, then you can ensure flushness. Once the component is flush, you can solder the other point. Then carefully trim the lead and move on to the next.
Troubleshooting: If you finish your board and one of the LEDs won’t light up, the #1 reason is due to an LED being placed backwards. Ensure you have your LEDs placed in the proper orientation before soldering to avoid that headache!
Step 5: Barrel Jack Board Connector
The final soldering point is your Barrel Jack Board connector. This is the connector that you use to connect the 9v battery to your board.
There is a component with three leads. It is not possible to place this incorrectly – there is only one orientation.
Place the barrel jack connector, and then solder one point. This component can suck up a lot of heat, so it may take a bit longer to get the lead to heat up enough to melt solder.
Once the first lead is soldered, ensure the connector is flush.
If it is, then solder the other 2 points. Again, this can take a bit longer due to the immense amount of heat required to heat up the leads.
Once you have it soldered, give your board a minute to rest. You have to put a lot of heat into the system to solder down this component. Let things cool down.
There are no leads to clip.
You’re now finished with the soldering. You can turn off your iron and your fume extraction.
Step 6: Stand-offs and Machine Screws
You’re almost done! The final step is to attach the stand-offs. There are four large holes at the corners of the board.
For each one, slide the machine screw through from the top of the board. Then, screw the brass stand-off on to the screw from the bottom.
We use these stand-offs to ensure that all of those solder points do not scratch up the surface we set our board on.
You’re Done! Now We Inspect
You’re all done soldering up your board! But before turning it on, go ahead and flip over the board and perform an inspection.
- Ensure that ALL soldering points are soldered. There should be no empty through holes.
- Check your solder joints. You want each one to be a nice little volcano-looking solder joint. If you have any bad solder joints, go ahead and clean it up.
- Check for any shorts – if you had any solder joints connect to each other, this can cause an issue with your board.
If you’re satisfied with your solder job, then you are ready to go! Flip the switch to off, plug in your 9v battery by attaching it to the clip, then plugging it in to the barrel jack board connector. Turn on the switch, you should immediately see some, but not all LEDs light up.
Logic Gates
You’ll see 7 logic gates on your board. The two buttons are your inputs. See what occurs as you push each button. If you press one or the other, you should see certain gates light up. If you press both, you’ll see other LEDs light up.
You can read the truth tables right on the board. It shows
Input A, Input B, and Output.
- Input A: The Tact switch on the left
- Input B: The Tact switch on the right
- Output: the LED in the associated gate on the board
The way to read a truth table is to look at Input A and B (which correspond to your buttons). 1 means you are pressing the button, 0 means you are not pressing it.
Compare those two states against the output. If the output has a 1, you should expect the LED to be lit. If the output is a 0, you should expect the LED to be off.
Example: I am pressing button A, but I’m not pressing button B. I look at the OR truth table. I find the row where A is set to 1, and B is set to 0. I then look at the output of 1. This means that the LED in the OR gate section should be lit.
Thank you for supporting eLearnTronics! If you have any questions at all, feel free to reach out to tron@elearntronics.com