Inexpensive Mechanical Shutter and Driver for Optics ... - Raizen Lab

Inexpensive Mechanical
Shutter and Driver
for Optics Experiments
Todd P. Meyrath 1
Atom Optics Laboratory
Center for Nonlinear Dynamics
University of Texas at Austin
c○ 2003 by Todd Meyrath
May, 2003
revised September 2003
Here we give a simple mechanical shutter and driver design that is reliable, fast,
and inexpensive (under $10 for a single shutter and driver). Complete schematics,
PCB layouts, and parts list are given in the pages that follow. There are two basic
versions given here which differ, principally, in the flag used to block the laser beam.
The basic idea is straightforward: an opaque flag is glued to a mechanical relay which
moves into (or out of) the beam.
Version 1: The flag is a small piece of folded aluminum foil which is glued to a small
wire which is, in turn, glued to the top of the moving flat copper contact of the relay,
see Figure 1. In test conditions given below, the performance of this relay is as follows:
throw 2 mm
closing velocity 1.7 mm/ms
opening velocity 1.5 mm/ms
time jitter ∼ 30µs
Version 2: The flag is a piece of a steel razor blade (or a small cut mirror for
high power beams) that is attached with epoxy to a solid 14 gauge copper wire, see
Figure 2. The extra length gives a much larger throw but the additional weight slows
it down. In test conditions given below, the performance of this relay is as follows:
throw 6.6 mm
closing velocity 0.7 mm/ms
opening velocity 0.5 mm/ms
time jitter ∼ 30µs
Definitions of the above: throw is the total distance that the flag moves, closing
velocity is the velocity of the flag when the relay is being switched on, opening velocity
1 Please send comments, questions, corrections, insults to meyrath@physics.utexas.edu
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is that when the relay is being switched off, jitter is the short time change in the
response of the shutter. Of course, the ‘opening’ and ‘closing’ depends on where you
place the beam. Here, we always assume that when the relay is switched on, the
beam is blocked.
Test: A 1 mm slit was cut into a sheet of paper which was placed directly behind
the flag. This was then illuminated by a large beam of roughly uniform intensity
over the test area. The exiting light was detected with a high speed photodiode and
oscilloscope. The velocity was nearly constant over the range of 1 mm aperture of
the test. The voltage used for this test was 20 V, see below. It was noted that speed
increases with extra voltage, however, this was not quantified.
Principle difficulty: The principle problem with a mechanical relay of this sort is
that, without modification, the shutter bounces when the relay is released (for about
10 to 20 ms in the case of version 2 - which has much worse bounce). It is simple to
solve this issue by removing the upper contact of the relay and replacing it with a
small piece of rubber sorbothane (www.sorbothane.com). In this case little bounce
was observed in version 2, and none in version 1. In our BEC experiments, this
problem presents no difficulty. Our pinciple application of these low cost shutters is
for beams that are intensity controlled by AOMs. The AOMs do very fast switch
off the beams with small leakage. The shutters described here are used to block the
leakage for during the long time evaporative cooling. In this application, neither
bounce nor timing is important. For this purpose, we used version 2 described here.
This has the added advantage of a black guard region along the beam path. Version
2 has also been used with a small cut silver mirror for beams with as much as 10 W
of power. Removing the lower contact pin adds a small amount to the throw.
On/Off delay: There is a delay in switching on and off of the shutter. The principle
delays are due to position of the beam with respect to the flag and the speed of the
relay. If the beam is very close to the flag, there will be a small delay for switching
off (2 to 3 ms version 1, 4 to 5 ms version 2) and a longer for switching on (8 to 10 ms
version 1, 12 to 15 ms) or vise versa. This was not studied in detail, except the jitter.
Driver circuit: The relay used has a nominal switch voltage of 12 V. The more
voltage the faster the shutter, within reason. Of course, one can not use a higher
voltage then 25 V in the design shown – the voltage of the large capacitor. Another
limit is the maximum gate-to-source voltage of the P-channel FET. We run at 20 V.
The shutter is normally open and the driver circuit uses a MOSFET to switch the
shutter off using a digital signal from a BNC which is not really necessary to be
50 Ω, a 1 kΩ input resistance is listed. The basic philosophy of the circuit is that
more current is required to close the shutter then to keep it closed. So current
initially comes from the capacitor which is charged to the supply voltage, which
gives current Iinit = Vsup/Rrelay. After the shutter is closed, current comes from
the power supply, but the voltage across the relay coil is lower so the current is
Iclosed = Vsup/(Rrelay + R3W). In our case, Vsup = 20 V, Rrelay = 155 Ω nominally,
R3W = 400 Ω, so Iinit ∼ = 130 mA and Iclosed ∼ = 36 mA. Initially, the driver circuit
supplies 2.6 W during the moment of relay closing and only 0.2 W while maintaining
the relay in a closed position. This is power that does not end up on the optical
table, which might have sensitivity to temperature drifts in beam paths. The power
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supply used is required to supply about 36 mA per shutter when closed. Otherwise it
is recharging the capacitors through R3W. Although when closed, only about 1/2 W
is burnt in R3W, a 3 W power resistor was used because the circuit may be used
for many different types of relays (and the author’s original relay had a much lower
resistance than the present one). The relay used is T90N1D12-12 from P&B Tyco
electronics (www.tycoelectronics.com), it is soldered to a small PCB.
Other designs: A different design for a low cost shutter is given in: Singer, et.
al., Review of Scientific Instruments, Volume 73, pp. 4402, 2002. This design is
based on a modified speaker and has slightly better specifications (same speed as
version 1 with 5 mm throw). Singer’s design has the advantage of nearly the throw of
version 2 presented here and the speed of version 1. However, Singer’s design has the
disadvantage of unpleasant modifications to a speaker as well as lack on any standard
part specification. The extra effort may be worthwhile if the improved throw is needed
on the faster version 1. Our design has the advantage of extremely easy construction
and little modification of widely available parts.
Parts: The boards used are presensitized PCBs to be exposed with a fluorescent
lamp, they were obtained from www.circuitspecialists.com. The layouts given were
printed on overhead projector transparencies and the boards exposed with a simple
fluorescent desk lamp for about 10 minutes. Most of the other parts were obtained
from www.mouser.com.
Parts for a single shutter and driver
Quantity Part Manufacturer Description
1 ZVP4424A Zetex P-channel MOSFET TO-92
1 2N7000 On Semiconductor N-channel MOSFET TO-92
1 RS-2B-400 Vishay Dale power resistor 400 Ω, 3 W
1 T90N1D12-12 P&B Tyco electronics SPST PCB mount solenoid relay
3 31-5538-10RFX Amphenol RF RA PCB mount BNC receptacle
1 UPW1E102MHH Nichicon 1000µF, 25 V Electro. Capacitor
1 SA30CA General Semiconductor 30 V Trans. Voltage. Suppressor
1 GD101 Ever-Muse, 100x150mm double-sided PCB
www.circuitspecialists.com
1 GS101 Ever-Muse 100x150mm single-sided PCB
1 1 kΩ 1/4 W resistor
1 50 kΩ 1/4 W resistor
Acknowledgements: The author would like to thank his co-workers on the Raizen
Lab’s rubidium BEC experiment: Florian Schreck, Jay Hanssen, and Chih-sung Chuu,
and of course Prof. Mark Raizen.
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Upper contact pin removed
rubber sheet added
attached wire
30 V TVS
Aluminium Foil Flag
Lower contact pin removed
Relay moving contact
mounting hardware
T90N1D12-12
Solenoid Relay
BNC receptacle
Figure 1: Shutter Version 1. The aluminum foil flag is attached to a small wire (cut
resistor lead) which is attached to the relay’s moving contact, both with 5 minute
epoxy. The upper and lower contact pins are easy to pull out before soldering. A
small 1/16 inch thick rubber sorbothane sheet is attached to the top of relay’s moving
contact by double sided tape.
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Hole for light
30 V TVS
solid 14 gauge wire
Razor blade shutter
Figure 2: Shutter Version 2. This version is basically the same as the previous where
the flag attachment has been replaced by a much larger wire to add more throw. In
this case, the flag is a piece of a steel razor blade that is attached with epoxy to a
solid 14 gauge copper wire. In cases of high power beams, we have used a small cut
silver mirror. Using the copper wire has the advantages of being pliable and can be
placed to be normally open or closed, but has the disadvantage of added mass. The
PCB and the flag were painted black for a reduction in scattered light. The hole can
be made any size.
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Figure 3: Driver Circuit. Four channels shown: Digital in, Drive Out, ... It is
suggested that box containing the circuit is carefully labeled with light and dark
stripes over the digital and the drive BNC receptacles – this will help to avoid the
obvious mistake which may damage the digital signal source.
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SOLENOID RELAY DRIVER
Each Channel:
1000μF
25V
+
400Ω 3W
ZVP4424A
+Vsup (15V to 24V)
S
50kΩ
to
Solenoid
S
2N7000
1kΩ
Digital
Input
Todd Meyrath
CNLD, Physics,
Univ of Texas
May 2003

Four Channel Solenoid Driver Layout
Dig In 1
50kΩ
N-Chan
S
400Ω 3W
3 circuits, 4 channels each
Four Channel Solenoid Driver Todd Meyrath May 2003
Dig In 1
1kΩ
50kΩ
N-Chan
S
400Ω 3W
D P-Chan
+
1000μF
Dig In 2
50kΩ
1kΩ
400Ω 3W
Top
D P-Chan 50kΩ D P-Chan 50kΩ
D P-Chan
GND
+
+ +
1000μF
Out 1 S Out 2 S Out 3 S Out 4
Four Channel Solenoid Driver Todd Meyrath May 2003
1kΩ
D P-Chan
+
1000μF
Dig In 2
50kΩ
1kΩ
400Ω 3W
Bottom
+20V
Dig In 3
+20V
1kΩ
400Ω 3W
D P-Chan 50kΩ D P-Chan 50kΩ
D P-Chan
GND
+
+ +
1000μF
Dig In 3
Out 1 S Out 2 S Out 3 S Out 4
Four Channel Solenoid Driver Todd Meyrath May 2003
Dig In 1
50kΩ
N-Chan
1kΩ
S
400Ω 3W
D P-Chan
+
1000μF
Dig In 2
50kΩ
1kΩ
400Ω 3W
+20V
1kΩ
400Ω 3W
D P-Chan 50kΩ D P-Chan 50kΩ
D P-Chan
GND
+
+ +
1000μF
Dig In 3
Out 1 S Out 2 S Out 3 S Out 4
1kΩ
400Ω 3W
1000μF
1000μF
1000μF
Dig In 4
Dig In 4
Dig In 4
1kΩ
1kΩ
1kΩ
400Ω 3W
400Ω 3W
400Ω 3W
1000μF
1000μF
1000μF

Board Layout for 10 relay shutters
Relay: T90N1D12-12 P&B Tyco Electronics
Bottom
Board Layout Version 1

Board Layout for 5 relay shutters
Relay: T90N1D12-12 P&B Tyco Electronics
Bottom
Board Layout Version 2

Bottom