LED Frequency Counter
Construction

LED Frequency Counter Circuit Details

LED Frequency Counter Connections for
the Salmon Pink Colored Boards Dated 10-1-2005

Construction of the PCB
Connecting to the Receiver (3/4/2015 Board) || Using the Frequency Counter
LED Frequency Counter Parts List

There were two boards made for this counter. Note the location of the 220 ohm resistors and click the picture of your board for instructions.

Construction of the PCB

Soldering Tips || To Cut or Not to Cut the Board
Construction of the PCB
Check Fix on the PCB
Step 1 - Resistors || Step 2 - Diodes || Step 3 - Capacitors
Step 4 - 2N3906 Transistors || Step 5 - 7805 and 10MHz Oscillator || Step 6 - PIC IC socket 28 pin
Step 7 - Solder 5 ICs || Step 8 - Solder two .01 caps || Step 9 - Solder the 7 LED displays
Step 10 - Solder the Headers - Display and Pic Boards || Step 11 - Insert the PIC16F72 into the Socket
Step 12 - Testing the Counter


Soldering Tips

The best soldering tip is use is a very narrow one. Check for pictures of some tips. A temperature regulated iron is the best to use.

Plated Through Holes

This PCB uses plated through holes. It is very difficult to remove parts from plated through holes unless you can remove one lead at a time. This means double checking all multiple pin parts (ICs, oscillator, voltage regulator, transistors) BEFORE soldering!

If you solder a part and realize it is in wrong, you have to cut all the pins off the part to get it out, which means getting a new replacement. Email and I will help with a new part.

Fitting/Soldering The ICs

The ICs have their pins flared out slightly. They will not fit into the board without a little adjustment. The pins need to be gently pushed in so they are straight down. This can be done with your fingers on each side of the IC pushing inward toward the middle of the IC. Go slow, check until they fit.

Hold the IC against the board with one finger, get some solder on the solder tip, then tack one lead of the IC to the board. Next, set the board down and solder another pin to the board feeding solder to the tip and pin and get a good solder joint.

With your finger against the top of the IC, holding it against the board, reheat both soldered pins to get the IC firmly against the board. Finally, solder the rest of the pins.

Large Soldering Tips

When using a solder tip larger than what is recommended, the best way to make it work is to start by placing the solder tip ABOVE the hole on the lead, get solder to flow on the lead adding some solder to the soldering tip and lead. Then move the tip down to the hole, keeping the tip against the lead, add a little more solder. The solder should be seen going into hole.

If you have a small round blob on top of the hole, try again, and check the top of the board to see if the solder has flowed through the hole.


To Cut or Not to Cut the Board

The board can be cut into two boards through the rows of holes in the middle of the PCB. See below.

Tin snips work well for cutting the board. It is recommended to start cutting as shown on the right side, as shown above, (when the board is populated) to prevent damaging the 6.8K resistor near the holes on the right side.

Cutting the board now, before populating the board, is a lot easier. However, you can change your mind later.

If tin snips are not available, a straight edge (i.e., a ruler) and a utility knife can be used to score both sides of the board through the holes. Go as deeply as you have patience for, then break apart.

If you are planning to mount the frequency counter between Board 1 and the bottom unetched PCB the boards need to be cut.

If you plan on building a case for the receiver and mounting the frequency counter on the front face, then you may not need to cut the boards depending on your design. Also, other projects may not require the boards to be cut.

Construction of the PCB

LED Frequency Counter Parts List

Check Fix on the PCB

It is so hard to make the perfect board; this one is no exception. Line "G" on the PIC board was extended so it shorted the 220 ohm resistor taking it out of the circuit.

Two problems resulted, a very bright "G" segment and it blew out the 4077 IC chip.

The fix is to cut the "G" segment line just above the bottom connection to the 220 resistor. This fix will be done before the boards are shipped, but it is a good idea to double check this fix before stuffing the board.

With a DVM on ohms, check for no connection between the "G" line resistor pads.

Arrows show where the leads of the DVM go to check fix.

Picture showing the fix on the bottom side of the board and pads to place the DVM leads to check the fix.

If you do get a connection between the two points, use a sharp knife, razor blade, or some appropriate instrument to make sure there is no connection between the pads of the 220 ohm resistor.

The location of the cut is important. The hole in the upper right of the small copper square of the fix must remained connected to the upper lead of the 220 resistor. If you get a board without the cut, make the cut in the same place as shown in the above picture.


Step 1 - Resistors

The footprints for the resistors have the value printed inside the footprint. Double check the value when inserting a resistor. Bend the leads of the 1/8 watt resistors about 1/16" from the body of the resistor to fit into the footprint. The leads of the 1/4 watt resistors are bent right against the body of the resistor.

1 - 10K, 1/8 watt, bend leads 1/16" from body

3 - 1K, 1/8 watt, bend leads 1/16" from body

4 - 100K, 1/8 watt, bend leads 1/16" from body

2 - 6.8K, 1/4 watt, gently bend leads against body

8 - 220 ohm, 1/4 watt, gently bend leads against body


Step 2 - Diodes

4 - 1N4148 diodes, bend leads 1/16" from body

Make sure the black band on the diode is inserted the correct way. The wide white band on the footprint is where the black band should go on the diode. To double check, the bands should be opposite each other at each pair.


Step 3 - Capacitors

1 - .1
1 - 2.2mfd electrolytic
1 - 100mfd electrolytic

Notice the electrolytics are polarized, they must be put in with the ground and positive side correctly. The short lead on the electrolytics is ground and the long lead is positive. The plus "+" side is marked on the board. Put them in incorrectly and they could explode or get very hot!

8 - .01, Note: Some kits may contain large .01 disc capacitors.

Start on the left side of the board and work around the top edge to the left side to get them all.

2 - .01 bottom side of board - Do not solder now!

This picture shows the location on the top of the board where two .01s are soldered underneath the board.

These will be put on the board in Step 8 after the ICs and 10 MHz oscillator have been soldered on the board.


Step 4 - 2N3906 Transistors

The kits have 7 - 2N3904s with straight leads for the LED cathode drivers and one flared (on a small piece of cardboard) for the crystal oscillator switch.

It is not necessary to push the transistors against the PCB. The footprint for the transistors was necessary because of the tight fit between the traces for the LED readout. As a result, a slight offset of the center lead is needed to fit the transistors in the footprint.

7 - 2N3906 straight leads

Insert 3 2N3906 in the top row. Notice the flat side of the transistor and match it to the footprint flat.

Solder the lower row of pins first. Then clip those leads so there is better access to the top row of leads. Solder the remaining leads.

Insert 4 2N3904 in the lower row. Match the flat of the transistor to the flat of the footprint.

Solder the lower row of pins first. Then clip those leads so there is better access to the top row of leads. Solder the remaining leads.

Check for solder bridges and bent wires shorting against adjacent pins after soldering and clipping all the transistor leads. Solder bridges can be easily removed by wiping the tip of the soldering gun between the pins.

1 - 2N3906 flared leads

Cut the transistor from the cardboard and insert in the place indicated above by the yellow arrow.


Step 5 - 7805 and 10MHz Oscillator

Location of parts. Please note the dots in the lower left hand corner of the 10MHz oscillator and the front and heatsink of the 7805 voltage regulator.

Be careful when inserting these parts, they must have correct orientation!

The 10 MHz oscillator can must have the dot in one corner at the lower left hand side as shown above in the picture. The dot is in the footprint and just outside so you can double check after the part is in place.

The 7805 voltage regulator must have the front of the part toward the outside of the board. Also, the front side of the part should be pointed to the part number "7805". The metal heat sink for the 7805 is the back of the part and should be toward the center of the board. See picture above.


Step 6 - PIC IC socket 28 pin

The orientation of this socket is important! Notice the notch on the right hand side of the socket.

The notch on the footprint and the notch on the socket should be seen together as shown in the picture.

Solder all the pins as shown in the picture. The arrows point to the beginning and end of both rows.

The one on the bottom left can easily be overlooked as there are other holes very close by.


Step 7 - Solder 5 ICs

The 5 ICs are soldered in this step. The most important part of this step is getting the notches correctly placed as shown on the footprints on the board.

There are 2 ICs that require special attention.

The first one is the 74AC151:

Pin 5 on the 74AC151 is cut off. Pull the pin out from the IC as shown above and cut it off. Pay particular attention to the location of the notch on the IC.

The picture above shows the location of the IC and the location where the pin is cut for. After the pin is cut insert into the board and solder.

The second one is the 4077:

It was a surprise to see this dot on the part at the wrong location! Insert this part according to the notch only! Ignore the dot.

Next, insert and solder the 2 74HC4046 and the 4066:

Be sure you have it right BEFORE you solder. Removing parts from plated through holes is very difficult.


Step 8 - Solder two .01 caps

This picture shows the location on the top of the board where two .01s are soldered underneath the board. At this time they will be covered up by the oscillator and 28 pin socket.

If you received large .01 disc capacitors with your kit, please click here for instructions. Click "Back" on your browser to return here.

The leads of two .01 caps are cut to 1/8". Insert the caps into the pads and solder. May take a little effort. To make it easier, be sure the width of the leads match the holes before cutting them short.

The Crystal Oscillator sets 1/8" above the PCB, enough to see if the leads of the cap are not touching the bottom of the oscillator. Double check to make sure the leads are clear of the oscillator.

There is little worry with the PIC cap as it is all plastic above where the .01 cap goes.


Step 9 - Solder the 7 LED displays

Look closely at the pin pattern of the readouts and it is obvious that the readouts will fit only one way. The notch is at the top of the readout and the decimal point is at the bottom right side.

The LED displays all soldered.


Step 10 - Solder the Headers on the PIC and Display Boards

The boards are connected back to back. The connecting pads are labeled 1 - 16 on both boards. Identical pin numbers are connected together. The back-to-back configuration gives easy access to the connections on the PIC board.

The headers can be soldered anyway you like. The following is my suggestion. The stronger headers are soldered on the PIC board in case a different display is used later on.

The male headers are soldered on the PIC board. The male headers have short pins on one side and much longer pins on the other. Solder the short pins onto the PCB, they fit perfectly.

Solder one pin of the header and then double check to make sure it is mounted 90 degrees to the board. Reheat the soldered pin if an alignment is necessary.

After alignment, solder the rest of the pins.

The female headers are soldered on the display.

Solder one pin of the header and then double check to make sure it is mounted 90 degrees to the board. Reheat the soldered pin if an alignment is necessary.

After alignment, solder the rest of the pins.


Step 11 - Insert the PIC16F72 into the Socket

Remember to bend the pins toward the center of the IC until they are pointing straight down. Look down the rows of pins to make sure one is not bent further toward the center than the others. If one is bent too far, it may bend against itself or against the bottom of the IC, not going into the socket correctly. This will cause an intermittent error when the counter is turned on.

Lay one side of the pins into the socket, do not push down.

Roll the other side of pins into the socket. They may not fit in. If they don't, push on the pins slightly with your finger until they slip into the socket. Or, bend them some more toward the center of the IC and try again. Be careful, go slowly.

Now push down on the IC to set into the socket. Look down each row of pins to make sure, as best as can be seen, that all the pins are inserted into the socket.

On the machine pin sockets, as shown in the PIC socket solder Step 6, a lot of pressure is needed to seat the PIC. Be sure the pins are all partially seated before pushing the PIC into the socket. If you are having trouble seating the PIC, try pushing down on one end while working your way to the other end.

If you do bend a pin, either up onto itself, or up against the IC, carefully straighten the pin. Reinsert the IC watching the previously bent pin to make sure it goes into the socket correctly. Using needle nose pliers makes straightening a pin easy.

You can get away with one rebending of a pin for sure, a second rebending of the same pin gets a little iffy, three, maybe not.


Step 12 - Testing the Counter

The "OSC IN" box is shorted to ground with a piece of resistor clippings as shown in the picture.

A couple of clippings are used to make connections for the "VFO In" and "GND". A couple more clippings are used to make connections for "12 Volts" and "Gnd" connections. The clippings are made into a tight U shape, inserted from the back side of the PIC board, twisted together, and soldered.

Another option is making loops, which will be easier to connect wires, can be made and inserted in all the necessary locations. See "Making Loops for Connections on the Boards". Click "Back" on your browser to return here.

The boards are connected together with the headers.


Apply a signal from a signal generator or the receiver VFO to the VFO IN and GND connections. While watching the display, apply 12 Volts to the 12 Volt and GND connections.

The first display to appear will be a single dot as shown above at the third digit from the right. The counter is reading the OSC IN signal.

About a second later, the OSC IN signal is displayed, which is 0.00 Hz (sometimes 0.01 Hz).

A second or two later, the counter now reads the VFO signal as shown in the picture.

If your counter follows the sequence above, then it is in proper working order.

The counter fixed this way can be used as a general purpose frequency counter for any project.

Disconnect the short across the OSC IN and Gnd connection before continuing to "Connecting to the Receiver".


Connecting to the Receiver

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Last Update: 4/17/2015
Web Author: David White, WN5Y
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