El Cheapo Assembly
The following procedures should be followed to set up and assemble the El Cheapo
programmer. In order to make sure that this operation goes as smoothly as possible, I recommend
that you get the El Cheapo Windows Interface up and running before you begin to assemble the
programmer. The five steps that should be taken before starting to build the El Cheapo programmer
are:
- Click Here to load the Port95NT Device Driver
- Click Here to load the El Cheapo Windows Interface
- Connect the Male to Male 25 Pin D-Shell "Parallel Transfer Cable" to the PC
- Plug the 14+ Volt AC/DC "Wall Wart" Power Supply in
- Click on "Start" -> "Programs" -> "El Cheapo Windows Interface" to start the El Cheapo
Control Software. Click on "Build/Test" to expand the display and show the assembly instructions
with testing options
The instructions in the "Build/Test" option will be used to guide you with which
parts are placed on the board at each step. I have built six different "El Cheapos" and this is the
order in which I have found the operations to be most efficient. You may encounter some problems
that you can't figure out. If this happens, look down at
Common El Cheapo Programmer Problems and their Solutions as your first
line of defense.
Warnings:
I do not have a stack of El Cheapo boards waiting to be sent to people who
incorrectly build their first ones. If you want a replacement board you will either have to buy
another book or have a quick-turn PCB house build what I am calling "PCB1". A little care at the
start will keep you from ruining the board or taking a long time to get it running. When you are
getting ready to build the programmer, here are some points to keep in mind:
- These instructions are designed to use a Digital Multi-Meter ("DMM") for verifying the circuit.
Chances are the board will work if you don't use one for assembly, but if you have a problem
you won't be able to find it without a Digital Multi-Meter.
- Use the Digital Multi-Meter for verifying resistor values. You can read the bands on the
resistors, but it is much easier to use a DMM.
- Make sure you have a PICmicro MCU chip handy for when the assembly is finished and you can
test out the programmer.
- Print out this page before you start assembling the board.
- If you are unsure about anything - ask!
- Much of the information that you will require is on this CD-ROM in the
Introduction to Electronics appendix.
- When you are asking questions, make sure you can describe the problems crisply - saying
that your El Cheapo board doesn't work won't get you very far. Read Chapter 12, "Debugging
your Applications" to help you look at the problems that you are having.
- The clerk at "Radio Shack" is probably not your best source of information or parts. If
you have questions, find an electronics technology instructor, send a request to a
sci.electronics newsgroup, the PICList, or, as a last resort, me.
- Using a "Straight Through" Male to Female DB-25 and a Male DB-25 Connector is NOT an
acceptable replacement to the "Parallel Transfer Cable" and the Female DB-25 Connector on the
board. "Straight Through" cables are generally designed for RS-232 applications and often do
not have all the pins connected. As well, using a "Straight Through" will reverse the pins
between the PC and the El Cheapo and will render the El Cheapo useless.
- Use the right tools for the job. Make sure you are using electronics soldering irons and
solder.
- Expect to take an afternoon to build and test this circuit. You won't need anything like
this, but it is always nice not to feel rushed.
I hope you understand that most of these instructions are common sense, but as
somebody much smarter than me noted, nothing seems to be so uncommon as common sense.
Once you have everything together and you are ready, follow the assembly
instructions below. Note that in virtually every step I ask for a voltage measurement and
occasionally a test operation from the PC - always disconnect the power and the PC after
testing the components for the current assembly step and going on to the next one.
- Get everything together. When I am about to start building a project, I like to place all
the parts in front of me. When this is done, click on "Next" on the El Cheapo Windows
Interface.
- Solder in the 2.5 mm Power Plug and the silicon diode at "CR8". When this is done, plug the
card into the wall wart and measure the voltage at "C8" as shown the El Cheapo Windows
Interface. The voltage must be greater than 14 Volts - Up to 18 Volts is not unreasonable. If
the voltage is very low (and can be measured very high at the plug), check the polarity of
"CR8" - the black band around the part should be pointing away from the Power Plug.
- Solder in the 10 uF (25 Volt Electrolytic) Capacitor at "C8". This capacitor should have a
band marked "-" down one side. This is the "negative" side of the capacitor and should not be
soldered toward the "+" marked via on the PCB. Next, Solder in "CR9" and "CR10" with the bands
pointing toward the Power Plug. Finally, Solder in the 78L12 with the flat side of the component
facing the center of the El Cheapo PCB. Plug the Power supply in and measure the power at the
points shown on the El Cheapo Windows Interface. If the voltage is less than 13 Volts, then
check the polarity of the diodes at "CR9" and "CR10" as well as the orientation of "U4".
- Solder in the 220W (1/2 Watt) Resistor at R12 and the 5.1 Volt
(1/2 Watt) Zener diode at "CR7". Note the power rating values for these two parts - this is
important to follow because the two components will dissipate quite a bit of power. When the
components are soldered in, plug in the power and measure the
output voltage as shown in the El Cheapo Windows Interface. If an incorrect voltage is
measured, check the component value of "CR7" as well as its orientation.
- Solder in the Female, PCB mount DB-25 Connector at "J2". Next, Solder in the 1K (1/4 Watt)
resistors at "R7" and "R9" along with the 0.01 uF capacitor at "C5". Solder in the diode at
"CR6" with the band facing away from the Power Plug. Finally, Solder in 0.1 uF Tantalum
Capacitors at "C6" and "C7". The two Tantalum capacitors should have a "+" symbol marked on
their body to indicate the positive pin - this pin should be connected at the via on the El
Cheapo PCB with the "+". To test the assembly of this circuit, connect power and the El
Cheapo to the Parallel Port "Parallel Transfer Cable" which is connected to the PC. The test
operation (click on "High" and "Low") can run autonomously, but I recommend checking the voltage
values between "R9" and "C5" with a DMM to make sure there isn't any kind of voltage drop
(caused by a "short" or "open" solder joing) within the circuit.
- Solder in the 10K (1/4 Watt) resistor at "R10". To test the assembly of this circuit, connect
power and the "El Cheapo" to the Parallel Port "Parallel Transfer Cable". Again, while the
software can test its own operation, I recommend using the DMM to ensure the connections are
behaving properly.
- To test the operation of the "clock" circuit, connect power and the "El Cheapo" to the
Parallel Port "Parallel Transfer Cable". There is no feedback circuit built into the El Cheapo
for this function, so you will have to use the DMM to make sure the Clock connection is
correct.
- Solder in the 10K (1/4 Watt) resistor at "R11". Next, solder in the 2N7000 transistor into
the circuit with the flat (labelled) side pointing towards the center of the card. Depending on
the manufacturer of the 2N7000, the labelled side may not seem to be the "flat" side - for this
component, always make sure the writing on the transistor is facing the inside of the card.
To test the operation of the "clock" circuit, connect power and the "El Cheapo" to the
Parallel Port "Parallel Transfer Cable". There is no feedback circuit built into the El Cheapo
for this function, so you will have to use the DMM to make sure the reset inverter circuit
connection is correct.
- Solder in the 330W (1/4 Watt) resistor at "R8". Next, solder in
the 2N3906 transistor into the circuit with the flat (labelled) side pointing towards the center
of the card. The same comments regarding "Flat" and "Labelled" side that were presented in the
previous step apply here. To test the operation of the "clock" circuit, connect power and the
"El Cheapo" to the Parallel Port "Parallel Transfer Cable". There is no feedback circuit built
into the El Cheapo for this function, so you will have to use the DMM to make sure the reset
inverter circuit connection is correct.
- Solder in the 18 and 14 pin sockets for "U5" and "U6", respectively. Note that if you are
going to use "ZIF" sockets, solder them in with the levers "up" (the socket is "open") to
minimize the stress on the pins and it will make them easier to use. If you find that the ZIF
sockets are stiff "reflow" the solder at each pin with the soldering iron with the socket "open"
(levers "up"). Next, cut one side away from a 28 DIP pin socket and mount it with its "inside"
facing the Female DB-25 Connector at "P28". When cutting the side away, make sure you trim off
the "supports" to the other side, to avoid interfering with the 40 Pin connector that will
soldered in the next step. When soldering in the "p28" connection, make sure the socket is
flat against the bottom of the PCB.
- The last assembly step is to cut away the "Pin 1" and center (if present) supports of a 40
pin DIP socket and solder it into the "P40" positions. This is a bit of a tricky step and
one that you can easily end up damaging the connector. To be on the safe side, I recommend that
you have two (or three) on hand in case you make mistakes (they should be quite inexpensive).
- With the El Cheapo assembled, I recommend that you program in an application (like
LEDOn) to test out its "functionality". When testing out the
programmer's functionality, remember to "verify" with a loaded and programmed device as well as
with a device programmed with a different application. You should be able to see the programmer
detecting validly programmed parts and failing invalidly programmed parts.
That's it for the El Cheapo PCB assembly. It is not a terribly hard PCB to build,
but if you are new to electronics, you should make sure you plan what you are going to do before
hand and don't do anything until you are sure that you're going about it correctly. If you are
running under MS-DOS, you will have to follow the same basic instructions, but use the "El Debug"
application.
Software Operating Instructions
Operation of the programmer is quite simple, regardless of whether you are running
under MS-DOS or Microsoft "Windows". For most people, I recommend that you use the Windows Interface
as this is the easier interface to work with and it will program calibration values and work with the
low-end ICSP programmed PICmicros quite intuitively. The MS-DOS interfaces are quite competent for
the mid-range devices, but I have yet to figure out a clear, intuitive set of command line parameters
for them to encompass different device types and features. If you have any ideas - please email
them to me.
Both El Cheapo interfaces execute at approximately the same speed. You may find
that the Windows version is even faster in some situations. Both interfaces program PICmicro MCUs
using the Microchip specified algorithms which are explained in the Datasheets
pages.
The MS-DOS "elcheapo.exe" application
is invoked with the following command line statement:
elcheapo ProgName[.hex] [/1|/2|/3] [/v] [/e]
Where: