Okotech DAC-40-USB User manual

OKO Tech DAC40 USB 1
DAC unit «DAC-40-USB»
Manual
1. Purpose
Digital-to-analog converter unit «DAC-40-USB» is intended to provide
multi-channel voltage output. It is controlled from a personal computer via a USB
port. Its primary purpose is to drive deformable mirrors produced by OKO
Technologies.
2. Specifications
V 1.0 V 2.0
Analog outputs 40 40
Output range 0 – 5.5 V 0 – 5.0 V
Output resolution 12 bits (4096 levels)
Range of adjustment of the maximum
output voltage
2.5 – 5.5 V 2.6 – 5.0 V
Ohmic load, each channel ≥100 kΩ≥100 kΩ
Load capacitance, each channel ≤500 pF ≤500 pF
Synchronous output for all channels.
Power is provided via the USB port.
3. General design
«DAC-40-USB» is designed as a PCB with two double-row angle
connectors BH-20R (male) and a B-type USB connector; it is mounted in a
compact housing. Pins of the output connectors are labeled according to the

OKO Tech DAC40 USB 2
numbering order of the output channels. The maximum output voltage value can be
adjusted (all channels simultaneously) by a variable resistor, whose slot is sunk in
a hole on the front side of the unit (Fig. 2).
To provide access to the PCB (Fig.1, 2) one should disconnect upper and
lower decks of the housing by simultaneous depression of their side surfaces. To
close the housing, the decks must be pushed vertically one to another till latched.
Fig. 1. «DAC-40-USB» view from the output connectors’ side
Fig. 2. «DAC-40-USB» view from the USB connector side
3.1. Jumper settings for version 1.0
Fig. 3. PCB layout and numbering of jumpers’ contacts for V.1.0
R
1
2
3
1
2
3
JP2 JP3
X3 X4

OKO Tech DAC40 USB 3
Jumpers JP2 and JP3 are mounted on the PCB (Fig. 3). By connecting
contacts 2 and 3 of jumpers JP2 and JP3 pin #1 of connector X3 (channel 1) and/or
pin #1 of X4 (channel 21), correspondingly, can be connected to the ground (see
Table 1). It should be kept in mind that when pin #1 of X3 (pin #1 of X4) is
connected to the ground, the 1st (or 21st, correspondingly) channel of the DAC is
disconnected from the connector.
Table 1
Jumper settings and output connectors commutation
JP2 Pin 1 of X3 JP3 Pin 1 of X4
1–2 Channel #1 output 1–2 Channel #21 output
2–3 Ground 2–3 Ground
3.2. Jumper settings for version 2.0
Fig. 4. PCB layout and numbering of jumpers’ contacts for V.2.0
Jumpers X3 and X4 are mounted on the PCB (Fig. 4). By connecting
contacts 2 and 3 of jumpers X3 and X4 pin #1 of connector X5 (channel 1) and/or
pin #1 of X6 (channel 21), correspondingly, can be connected to the ground (see
Table 2). It should be kept in mind that when pin #1 of X3 (pin #1 of X4) is
connected to the ground, the 1st (or 21st, correspondingly) channel of the DAC is
disconnected from the connector.
Jumpers X7 and X8 allow swapping pins 1 and 2 of the output connectors
X5 and X6 (see Table 2 for details).
Jumper X9 can be set to connect the outer case of the USB connector X2 to
ground.
direct
cross
1 2 3
X3
X
7
direct
cross X4 1 2 3
X8
X5 X6
X9
X2

OKO Tech DAC40 USB 4
Table 2
Jumper settings and output connectors commutation
4. Getting started
Before using the unit, it is necessary to check settings of jumpers or
appropriately configure those according to specifications of connected device(s) as
described above.
To put the unit into operation following steps must be done.
•Plug connecting cables into the output connectors of the unit.
•Connect the unit to the USB port of your PC using the USB cable. The
LED lit on the USB port face in 2-2.5 seconds indicates normal
operation of the unit.
•Install FDTI Direct Driver for Windows 98/2000/ME/XP from the
folder /Drivers of the supplied software CD. Updated drivers can be
downloaded from www.ftdichip.com. For version 2.0 you have to use
the driver version 2.00.00 or higher.
•Run TEST_DAC40.EXE, move the pointer of the output voltage into
Umax position, then adjust the output voltage to the required value by
rotation of the spindle of the variable resistor R. The level of the
output voltage must be measured by a voltmeter connected to one of
the output pins with respect to the grounded pin.
5. The program interface
5.1. General
Data transfer between PC and DAC via USB bus is managed by the interface
chip from FT245 series. To provide necessary speed of data transfer between PC
and DAC it is necessary to use FDTI Direct Driver. The corresponding program
interface is implemented in the library FTD2XX.DLL.
5.2. Application of the library FTD2XX.DLL
To provide access to the DAC, the following functions of FTD2XX.DLL
are implemented:
X3 X7 Pin 1 of X5 Pin 2 of X5 X4 X8 Pin 1 of X6 Pin 2 of X6
1–2 Ch #1 output Ch #2 output 1–2 Ch #21 output Ch #22 output
2–3 direct Ground Ch #2 output 2–3
direct Ground Ch #22 output
1–2 Ch #2 output Ch #1 output 1–2 Ch #22 output Ch #21 output
2–3 cross Ch #2 output Ground 2–3 cross Ch #22 output Ground

OKO Tech DAC40 USB 5
•FT_ListDevices – allows to detect the number of connected devices,
their serial numbers and specifications;
•FT_Open – opens of the device for data transfer;
•FT_Write – send a packet of control data from the PC to the device;
•FT_Close – closes the device.
Specifications of these functions are given in the programmer’s manual of the
library FTD2XX (file D2XXPG33.pdf in the folder /Driver of the software CD).
Examples of their use are given in Section 5.4.
5.3. Data interchange via USB
Control of the unit from an external program is organized by sending data
packets to the module. The data packet has 129 bytes size. An example of forming
of the data packet from an array of 16-bit values corresponding to output voltages
of the DAC unit is given in Appendix 1, function MakePacket.
When the data package is received and control words loaded into DAC
chips, synchronous setting of signal levels at the outputs takes place, and the
micro-controller enters the standby mode, waiting for the next data package. In this
mode, zero bytes transferred into the module via the USB bus are ignored. In order
to put the unit into the standby mode, it is necessary to fulfill transfer of data
package consisting of 128 zero bytes. It is recommended to perform this operation
when initializing the unit’s control cycles.
5.4. MakePacket function usage
To facilitate programming of the unit, one may use the function
MakePacket. It transforms an array consisting of 40 two-byte words, each of them
coding an output voltage at the corresponding channel, into the data packet, which
can be transferred via USB. Text of the function and an example of its usage are
given in Appendix 1.
When connecting two or more DACs «DAC-40-USB» to the computer it is
necessary to define their system numbers by means of FT_ListDevices function. A
detailed description of this function is given in file D2XXPG33.pdf, folder
/Driver in the software CD. An example of usage of function FT_ListDevices is
given in Appendix 2.
For synchronous control of the units one may use the function MakePacket.
It is implied that before this all devices «DAC-40-USB» are opened by means of
the function FT_Open, with preliminary defined system numbers of these
modules.