PatchJet - User Guide
works of  Carl C Pisaturo
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Tubing to Pipettes
Use 1/8" OD "firm" tubing, transluscent or clear, for runs to pipette holder, and keep runs short as practical to optimize temporal response of pressure pulses.  Remove back cover to attach/detach to PatchJet's push-to-connect fittings.   
Warning LED: Sucked Saline
If a PatchJet channel is in either suction mode (NEG or BRK) and the electrode tip is broken, saline could be drawn up the output tube. If this saline was allowed to enter PatchJet internals, damage is likely.  That's why there is a system to prevent saline uptake and warn user.  This self-protection system (photo right) consists of a verticle water "trap" column with a water sensor at bottom, automatic circuitry and a blinking red warning LED. If water is detected in the trap, the PatchJet switches into NEU and LED blinks.  User must blow liquid out of the tube using POS.   The trap is clear plastic and can be seen at the rear of the unit, this along with clear output tubing allows observation of the blow-out process.     


Warning LED: Bad Pressure
If the output pressure observed by an onboard pressure sensor is clearly wrong for the current mode, LED will light. 

For POS and PUF, the LED lights if output is  < +0.5 psi.
For NEG and BRK, the LED lights if output is  > -0.5 psi.
For NEU, LED lights if output > +0.2 psi or < -0.2 psi.

NOTE: LED will flash during transitions, as there are a few milliseconds out-of-range as pressure/suction builds towards final value.

This warning will flag major problems such as:
a) house air of vac is turned off
b) regulator failure
c) solenoid valve failure
d) tubing / connector issue 
Debug Mode: Charge and Hold
Charges the output to PUF pressure then shuts off all valves. 

This is a leak test of a lot of important things: structures, valves and connectors within the Patchjet itself, output tubing, pipette holder, pipette.  You can read the Pressure Monitor BNC with a multimeter set for DC volts.  The system gets a "pass" if the output pressure stays steady for, say, 1 minute.

If the output pressure changes, it's a "fail" - indicating that air is leaking out somewhere.  A good divide-and-conquer step to locating the leak is to plug the PatchJet output (use a 1/8" diam stainless steel dowel pin) and try again.  If leak persists, PatchJet module is faulty and must be serviced, if leak disappeared, downstream components are at fault.



Debug Mode: Valve Test Pattern
Operates the PatchJet valves automatically so user can focus on observing output pressures and internal LEDs to confirm correct operation or locate faults.  

The modes will cycle at 1/2 Hz NEU-POS-NEU-NEG-NEU-BRK-NEU-PUF, etc.  Press NEU to exit test.  Observing the Pressure Monitor on an oscilliscope, correct operation will show as a clear pattern (photo right).

User may also observe LEDs on solenoid valves to confirm they are being triggered as expected.
Electronic Output Pressure Monitor
Each PatchJet channel is fitted with an MPXHZ6250A absolute pressure sensor.  This device converts output pressure into a 0-5V analog voltage available on the BNC connector.  The output may fed to a multimeter to get a numeric value representing pressure;  oscilloscope to see time-course of pressures; and digitizer to create a "pipette pressure" data field in an experiment. 

Typical NEU (atmospheric pressure) voltage is 1.84V.
+5 psi    gives about 2.55V
-15 inHg gives about 0.9V




Using Pulse Generator
The pulse generator module (bottom panel) generates  a positive or negative pressure pulse on a channel set to BRK or PUF when FIRE button pushed. 

User sets pulse duration in milliseconds via the 3 up/down toggles, one toggle per digit. 

Two nonvolatile memories are provided for commonly used values.  When PatchJet powers up, the value in the top memory is loaded. 

25 mS is the minimum pulse value - as fast as these  solenoid valves can handle.   999 mS is maximum.

The above refers to MANUAL control...  By the toggle on the right, the pulse generator can also be set to EXTERNAL, in which case a 5V logic signal from an external device controls the pulse directly. 

When the pulse generator fires (either manually or externally controlled), FIRE LED lights for the duration of the pulse.  If a channel mode is set BRK or PUF, that channel will switch into BRK or PUF then return to NEU when pulse completes.  If no channel is set BRK or PUF, nothing will happen during pulse, and no solenoid action will be audible.     
 
RAPID FIRE pulses can be done, although with a small reduction of pressure/suction each subsequent pulse.  The air-cans supply the pressure in the short term while the pressure regulators slowly bring air-can back to setpoint.
Selecting the Ouptput Pressure Mode
User selects output pressure mode by pushing one of the 5 mode buttons:  NEU = "Neutral", or open to atmosphere.
POS = "Positive", keeps tip clear during pipette movements.
NEG = "Negative", pulls cell towards pipette.
BRK = "Break-In", applies suction pulse when pulse generator fires.
PUF = "Puff", applies positive pressure pulse when pulse generator fires.
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MODE MAY CHANGE AUTOMATICALLY UNDER FOLLOWING CONDITIONS:
1) Only one channel is allowed to be in BRK or PUF mode at a time. If another channel goes into BRK or PUF, original channel goes into NEU. 
2) If water is sucked up, channel goes into NEU and "sucked saline" LED activates.  NEG and BRK not allowed until water cleared from trap.
3) During debug modes.
Setting up the 4 Pressures  (POS, NEG, BRK, PUF)
Adjust knobs while watching gauges to set the 4 pressures.  BE PATIENT, it takes several seconds for the pressures to stabilize and there is hysteresis when changing direction.  Right = more pressure, more suction.  Don't set higher than gauge can go.  Note: BRK suction will be limited to 3 inHg weaker than supplied "house vacuum". 

Some underlying detail... The compressed air fed into PatchJet goes to 2 precision pressure regulator units (Airtrol R-900-30, McMaster Carr # 43275K36). These units attempt to keep output at a constant pressure, as set by user with knob. This is an impressive feat for a mechanical device, but there are caveats with all (and especially miniature precision type) pressure regulators:
a) They take time to respond to output variations - that's why there are "air cans" to minimize output pressure variation as use happens.
b) When user changes setpoint, they are slow to stabilize and have hysteresis when changing direction.
c) They consume some air, even when stable. 
d) Output changes slightly as input changes.
 
Size and Weight
Weight = 19 pounds (8.6 Kg).  Enclosure size:  width= 8 3/8" (212 mm), height = 17 3/8" (442 mm),  depth (including gauges) = 10 1/2" (268 mm)
Mounting
Preferred method is "pivot mounting" (photos right), either left or right, to verticle surface using supplied L brackets.  The PatchJet's sturdy aluminum frame has trios of 1/4-20 tapped holes top and bottom, with 3" pitch.   A T-slot framed faraday cage around rig is an ideal thing to attach to. Using adjustable handle studs, user can attach and rotate PatchMaster, allowing ideal ergonomics.  CAUTION: TOO LONG SCREW ON BOTTOM CAN DAMAGE PULSE GENERATOR. Rear access should be maintained.

Method 2)  Set PatchJet on table or shelf, w/ or w/o safety screw.
Method 3)  Hang PatchJet from above using tapped hole(s)    
(left above) Attaching "L" brackets to T-slot framing, with 442 mm clear space between. (right above) PatchJet is positioned onto brackets and secured with adjustable handle studs.
Power and Ground
Three power cords must be plugged in.
Two are "wall warts" for the pressure switch modules, and one is for grounding (wall warts don't bring ground to devices).  Although less tidy than a central power supply, this design strategy allows the modules to be fully independent  -  a big plus during build, testing and repair.  Each module must be switched "ON" to use. NOTE: The pulse generator obtains power from its neighbors if one or both are powered on.
Compressed Air and Vacuum Supply
The PatchJet must be supplied with compressed air and vacuum, attached at back / bottom of unit.

CONNECTORS: 1/4" OD push-to-connect type.  To insert a tube: push firmly till stops. To remove tube: push black ring while pulling tube (it should come out pretty easily). 

TUBING: use 1/4" OD "firm" tubing, e.g. McMaster-Carr 5648K69. NOTE: Tygon, a "soft" tubing, is not appropriate for these fittings.

SOURCE: "House Air" and "House Vaccum" are typically available in   laboratory settings and preferred.  It is possible to use your own compressor and vacuum pump, but noise considerations must be appreciated.   

CONDITIONING: compressed air must be dry and filtered to 5 microns. All rooms with precision air-driven equipment (including air tables) should have a device like this to prepare the air.   

+PRESSURE: compressed air can be 20 psi to 100 psi.

-PRESSURE: must be 3 inHg stronger than desired BRK value.

CONSUMPTION: PatchJet's regulators consume air and vacuum.  It's advisable to shut off supplies when not in use.  While this consumption is a tiny load for house air and vacuum systems, it matters if local compressors are used since they will loudly recharge periodically.    
User entering a debug mode by pressing recessed button with wood or plastic stylus.  Press NEU to exit.
Viewing the Pressure Monitor during Valve Test Pattern with an oscilliscope: A healthy PatchJet displays this typical pattern, amplitudes will vary with your pressure settings. 
PatchJet water trap module close-up (above) and context (left).

Sucked up saline enters trap column at bottom and triggers water sensor. Suction is halted so saline cannot reach top connector.

Pressure sensor is also mounted to this block.
PatchJet - Overview