# Printed Circuit Boards now available!!!

Pat Sweeney has designed a pcb for the computerized altazimuth newtonian project.

I have printed circuit boards both populated and unpopulated. The opto-isolator circuit, the field derotator circuit, and the main driver circuit, are on the 5.7" x 6.1" sized board. A parts list and layout graphic are included.

Pat Sweeney is populating and testing some of the printed circuit boards (the field derotator portion of the printed circuit board is left unpopulated).

I am charging $25 per unpopulated board plus either $5 for US shipping or $10 for overseas shipping.

I am charging $65 per populated and tested board (the field derotator portion is not populated) plus either $5 for US shipping or $15 for overseas shipping.

Mel Bartels
1294 B Street
Springfield, OR 97477 USA

## Parts List and Assembly Notes:

#### units used:

all capacitors are in microfarads;
all resistors are 1/4 watt;

#### part selection:

there is a fair degree of latitude in selecting parts;

#### heatsinks:

no heatsinks are required on the power transistors as the software ensures that only the needed current is sent to the motors, for instance, 1 amp motors typically draw 0.1 amps while tracking and slewing;

*** note by Pat Sweeney: I found that if the motors draw less than 1 amp each the transistors do not get hot while slewing or tracking. Currents of 4 or 5 amps while ramping up or down also are OK. If currents of around 2 amps per motor are expected. insure cooling via a small fan blowing on the TIP120s If currents much above 2 amps are expected I would suggest heat sinks But they must be electrically isolated. the collectors are tied to the tab on the TIP120s ***

#### power/ground connections:

the 6 holes for power and ground go as follows (board face up with the 6 holes to the lower left):
gnd
+5 vdc
gnd

+12-24 vdc
gnd
+12-24 vdc

for complete isolation, use separate computer and motor grounds, and supply an external +5.0 VDC source for the computer side;
the vast majority of us will not require this total isolation, instead, tie computer and motor grounds together, and supply the computer +5 VDC from the bottom lead of U6;

*** note by Pat Sweeney: I left the computer 5volt supply separate from the 12-24 volt supply to isolate the parallel port from the drive circuit. If a catastrophic failure on the drive circuitry occurs there is the possibility of wrecking the parallel port on the computer. If + 5 volts is not available from the computer for this then I suggest using a small isolated DC to DC converter off the 12-24 volt side. I found a 12 to 9 volt 250 MA ,DC to DC converter from JAMECO Part # 153736
$1.95 and a 5 volt regulator will provide the isolation for my laptop. ***

#### 9/25 pin connectors:

circuit board 9 pin and 25 pin connectors are straight (not angled) connectors; use thin flat cable to connect these to a set of connectors that you have mounted in the electronics box's face plate;

*** note by Pat Sweeney: you can mount all but the 25 pin parallel port connector from underneath on the solder side ***

#### config.dat settings:

set InvertOutput to 0 in config.dat.

Original designed called for 7404 inverters to drive the transistors, hence InvertOutput 1 in the original config.dat (parallel port output goes high, hex inverters go low, and drive transistors turn off, hence the need to invert the output).
In the original design, if opto-isolators were used, then InvertOutput 0 (parallel port output goes high, hex inverters go low, opto-isolators turn on pulling output low, hex inverters go high, and drive transistors turn on, hence no need to invert output).
This pcb design uses 7408 and gates (parallel port output goes high, 7408 and gates go high, opto-isolators turn off allowing output to return to high, 7408 and gates go high, and drive transistors turn on, hence no need to invert the output).

#### field derotator:

the optional field derotator SAA1042 can be added later;

*** note by Pat Sweeney on the field derotator portion of the pcb ***
The schematic and silk screen does show the 3.9 volt zener in backwards. (sorry ) The rest of the circuit is OK. The chip is configured to drive a 2 phase bipolar stepper motor. (4 wire motor) I tested the circuit on a stepper that draws 200MA per winding and it seems to work properly. Only the pins 6,7,8,and 9 are used. Pins 1,2,3,4, and 5 can supply + 12 volts for external transistors to power a stepper that will draw more than 500MA. Ground for external transistors will have to be supplied from another location on the board.
I wrote a program fldrot.exe (download fldrot.zip here) that will run from DOS or WINDOWS 3.1 & 95 . It will step a bipolar motor 1 step per second for 200 steps forward and then 200 steps in reverse and continue in this mode until "Q" is pressed. It should help in debugging the circuit. Note don't have the ALT or AZ motors attached while using FLDROT.EXE.

*** note by Chuck Shaw on how to modify the field derotator portion of the pcb for a unipolar stepper ***
select here for Chuck's note
select here for Chuck's circuit mod
select here for Chuck's pcb mod graphic #1
select here for Chuck's pcb mod graphic #2

#### handpad and parts list:

here's the handpad circuit diagram

1 small plastic box about 4 inches (1.5cm) x 2.5 inches (1cm) x 1 inch (.5cm) in size
4 momentary push buttons - normally off, temporarily on
1 3-way center-off switch (can be spring loaded to return to center position)
1 2-way switch
6 small diodes

Here's how Ned Smith built his handpad:
I used the following from TechAmerica: 910-1075 $15.48 It is a 1 x 2.4 x 3.8 inch enclosure with a membrane
switch pad. It has a 3 x 4 switch array. I cut off one row to make a 3 x 3. This gives me Up, Down, Right, and Left. I used the upper R and L corners for the for the self-centering toggle switch. I only had to add SPDT to handle the two stepping rates. The membrane switches add about 50 ohms to the circuit which reduced the voltage at the connector. I used RJ12 connectors for the hand paddle to PCB enclosure and stepper motor to enclosure.

#### circuit board and parts list:

here's the printed circuit board circuit diagram

use the part numbers here and on the printed circuit board - any part numbers on other circuit diagrams do not necessarily correspond to the pcb, click here for parts layout

`1 C1 4.7/35V tantalum cap`
`1 C2 47/35V electrolytic cap`
`6 C3-C8 0.1 monolithic cap`
`1 D1 3.9V/1W zener`
`8 D2-5, D7-10 1N4004 small signal diode`
`4 D6, D11-13 30V/1W zener`
`10 ISO1-10 4N26 optoisolator`
`1 P1 DB25F connector`
`3 P2-4 DB9F connector`
`2 Q1-2 2N2222 transistor`
`8 Q3-6, Q9-12 TIP120 transistor`
`4 Q7-8, Q13-14 MJE3055 transistor`
`14 R1-4, R6, R10, R12, R14, R17-18, R26-27, R29, R31 220 ohm resistor`
`1 R5 56k resistor`
`11 R7, R9, R13, R15-16, R19, R24-25, R28, R30, R38 4.7k resistor`
`4 R8, R11, R32, R37 2.2k resistor`
`8 R20-23, R33-36 470 ohm resistor`
`1 RJ11 RJ11 connector`
`1 U1 SAA1042 IC` (needed only if you will be doing field derotation, obtain from Newark Electronics http://www.newark.com)
`4 U2-5 74LS08 IC`
`1 U6 7805 regulator`

Current Limiting Addition by Jean-Charles Vachon

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...by Mel Bartels