16 Channel Digital Output
Todd P. Meyrath1
Florian Schreck
Atom Optics Laboratory
Center for Nonlinear Dynamics
University of Texas at Austin
c 2004 by the authors
December 14, 2003
revised May 27, 2004
Here, we present the design of a 16 channel digital output for use with the bus
system described at the authors’ website:
george.ph.utexas.edu/~control
The basic features are as follows:
• Each channel is a single bit of output of a 16-bit device
• Addressable on a simple bus system.
• Each channel has line drive capacity to drive 50 Ω loads
• Convenient setup for laboratory electronics with BNC outputs
The circuit is relatively simple to understand from the schematic and is competitive with professional output boards such as those produced by National Instruments.
This design is the digital compliment to the analog (DAC) device also described at
the authors’ website. The cost per board is roughly $65 ($40 for the board, $5 for
the ICs, transistors, and passives, $20 for the BNC receptacles).
The Printed Circuit Board:
The PCB is a four layer board with signal lines on the top and the bottom. The
second to the top layer is the location of the ground plane the third from the top is the
power plane (+5 V). All ICs are located on the top as well power connector and ribbon
cable connector. The vertical BNC receptacles are located on the bottom, making the
board simple to front panel mount. The PCB was designed using the free software
from PCB123, this company produced our circuit boards. For the design presented
here, the PCB cost was about $400 for 10 boards including silk layer charges. The
software and information is available at the web site www.pcb123.com. The design
of the board is shown in the printout pages near the end of this document and the
design file is available at the author’s website.
1
Please send comments, questions, corrections, insults to meyrath@physics.utexas.edu
1
Circuit Theory:
This circuit is simple to understand. The input consists of a 50 pin input header
for a 50 conductor ribbon cable. The signals are spaced with ground lines between
them giving 25 digital signals. The first 16 are the data bit lines, the next 8 are
the address bus lines, and the final line is the strobe bit. The logic circuit works as
follows. The strobe signal enters the comparator and is sent out if the local address
matches. In this case, the strobe passes the comparator to command the latches to
accept and hold the new 16 bits of data. Note that, for the DIP switches, the ON
position indicates a LOW and the OFF position indicates a HIGH as far as the board
address is concerned. The function of the latch is to have memory. The each latch
holds old data in a buffer until it is commanded by the comparator’s strobe to accept
new data. Here, the new data is held until the next command to this board. All 16
digital outputs may be updated each clock cycle. The transistor line driver circuit is
also a standard 50 Ω cable driver2
2
4
6
8
10
12
14
16
18
20
22
24
26
28
30
1
3
5
7
9
11
13
15
17
19
21
23
25
27
29
LSB
32
34
36
38
40
42
44
46
31
33
35
37
39
41
43
45
MSB LSB
16-bit data bus
odd 1 to 31
8-bit address bus
odd 33 to 47
strobe bit
ground line
48
50
47
49
MSB
49
even 2 to 50
Figure 1: Pin configuration for 50-pin connector.
2
see Figure 9.42 pg. 612 The Art of Electronics 2nd Ed. Horowitz and Hill. Cambridge Univ.
Press 1989.
2
Figure 2: A completed board, both sides.
3
Figure 3: A completed board, a different view.
4
Parts
Qu. Label
Part #
Manufacturer/Description
4
C1-C4
140-CC502B104K
Xicon / 100 nF cap, 1206 chip pkg.
1
C5
470 µF electrolytic capacitor 25 V
2
C6, C7
T491A106M016AS
Kermet / 10 µF solid tantalum surface mnt.
2
U1, U2
SN74ALS573C
Texas Inst. / 8-Bit Latch, 20-SOIC wide pkg.
1
U3
CD74HCT688M
Texas Inst. / 8-Bit Mag. Comp., 20-SOIC wide pkg.
1
U4
SN74LS14D
Texas Inst. / Hex schmitt-trigger inverters, 14-SOIC pkg.
16 Q1 to Q16
2N4401
Fairchild Semi / NPN transistor, TO-92 pkg.
16 R1-R16
CRCW1206510RFKTA Vishay/Dale / 510 Ω 1260 pkg resistor.
16 R17-R32
CRCW120610R0FKTA Vishay/Dale / 10 Ω 1260 pkg resistor.
8
R33-R40
CRCW120610K0FKTA Vishay/Dale / 10 kΩ 1260 pkg resistor.
16 J1 to J16
227222-1
AMP-Tyco Elec. / Vertical PCB mnt BNC receptacle.
1
J17
1-103308-0
AMP, Tyco / 50 pos. header.
1
J18
70543-0002
Molex / 3 pin vertical header power conn.
1
50-57-9403
Molex / 3 pin mate housing.
16-02-0102
Molex / female crimp pins.
1
S1
SDA08H1KD
ITT Ind. / 8 pos top slide DIP switch, 16-DIP pkg.
Quantity is per board, label is on the PCB, part # is manufacturer number. Most parts obtained
from www.mouser.com, www.digikey.com, or www.alliedelec.com.
Acknowledgements: The author would like to thank his co-workers on the
Raizen Lab’s rubidium BEC experiment: Florian Schreck, Jay Hanssen, and Chihsung Chuu, and of course Prof. Mark Raizen. Florian’s experience and suggestions
were invaluable on this project.
5
16 DIGITAL OUTPUTS
Todd Meyrath
CNLD, Atom Optics
Univ of Texas
Nov 2003
updated v1.1 March 2004
1/6 SN74LS14
strobe
U4
2
1
1
8 Bit
Address
Bus
2
4
6
8
17
15
13
11
E
CD74HCT688M
8-Bit Comparator
MSB
S1
U3
3
5
7
9
18
16
14
12
A=B
LSB
DIP Switch
local address
set
+5V
out
10kΩ
R33 to R40
1/6 SN74LS14
19
13
U4
Additional Connections:
12
+5V
2
3
4
5
6
7
8
9
+5V
Line Driver
U2
11
SN74ALS573C
8-Bit Bus Latch
LE
Can drive 50Ω load
19
18
17
16
15
14
13
12
OE
R17 to R32
Each of 16 Outputs
10Ω
C1 to C4
10nF
Q1 to Q16
2N4401
R1 to R16
Digital
Output
BNC
500Ω
Digital IC
J1 to J16
1
16 Bit
Data
Bus
11
LE
SN74ALS573C
8-Bit Bus Latch
U1
2
3
4
5
6
7
8
9
OE
1
19
18
17
16
15
14
13
12
+5V
C7
C6
C5
+
470µF
+
10µF
+
10µF