PneuMatic - Tyre Pressure Control

Bluetooth Online Tyre Inflator/Deflator

Deflated to 100kPa
Floating on 100kPa


Why is Online Wonderful?

Mobility. A heavy-duty compressor is tethered to it's power source by a short, thick cable.  With online remote control you can set your camping stool by the wheel and bring the tyre pressure up or down to exactly where you want it by moving only your fingertip. No more back and forth between compressor switch and pressure gauge.

Convenience. You can relax in your vehicle, sheltered from the elements, while Auto Mode arrives at your chosen pressure at the touch of a single button. (It helps to have a volunteer assistant to move the hose from wheel to wheel.)

Needs Help
This One Needs Your Help

The PneuMatic Pressure Control System makes this process as hassle-free as it is possible to get. Someone still needs to move the hose from wheel to wheel, but everything in between is either automated or done while seated within vehicle.

The PneuMatic Control Unit is an intelligent device that can switch a compressor on and off, electronically open and close a deflator valve, and measure hose pressure in an air hose connected to a pneumatic tyre. It is contained in a plastic housing that is designed to be mounted in the corner of a larger container that also houses a 12V compressor, an air hose, and other tyre maintenance accoutrements.

The control unit takes instruction from and reports to a mobile phone app via the Bluetooth communications medium. 

The Control Unit
The Control Unit
The control unit has connections for:
  • An air hose that also connects to the compressor and tyre valve.
  • A pair of  Anderson SB50 (50A) connectors that serve as power input and output These connectors are wired to power relays with 60A switching capacity. Either connector can act as input or output. Controller power is drawn from whichever is hot. Connecting the In and Out cable to each other bypasses the controller when needed.
  • There is a deflator vent port to release air from the deflation operation
The mobile phone app has the facilities to:
  • Display hose pressure (equal to tyre pressure when at rest).
  • Display battery voltage as measured at the compressor - where the cumulative effect of the many volt-drops in the power supply become apparent.
  • Display the battery current drawn by the compressor - the reason the measured voltage is so low.
  • Display the compressor On or Off
  • Display the deflator Open or Closed
  • Set Target Pressure,
  • Display time to end of inflation/deflation phase.
  • Select 1 of 5 tyre size groups: V-Small, Small, Medium, Large, X-Large,
  • Select 1 of 5 compressor size categories: V-Small, Small, Medium, Large, X-Large, spanning compressor capacities from 30LPM to 180LPM (App V3.1.0 and up).
  • Display Bluetooth connectedness
  • Switch the phone's flashlight
It has buttons to:
The Complete Set
The Complete Set
  • Start and stop the compressor
  • Open and close the deflator valve
  • Initiate and end an automatic inflation/deflation operation
  • Adjust Target Pressure between 100kPa and 350kPa. 
  • Select Secure Mode or Free Mode.
  • Calibrate the Pressure Sensor to ambient pressure.

The larger housing (a 50L ammo box is a popular option) should also contain a compressor of a quality and capacity sufficient for the job, up to 10 metres of silicone rubber air hose, a mechanical pressure gauge on the air hose as a backup measure, and optionally tyre repair and patching gear, a backup foot pump, tyre levers, etc.

In case of the Bluetooth control system not being operational for any reason the input and output plugs may be connected so as to by pass the control unit, and the air hose with its self-sealing coupler can be detached as well, closing that end of the hose.

To allow the box lid to be used to coil the air hose it can be hinged at the rear edge with the type of piano hinge available at any hardware store. A string restraint can limit the lid's opening travel, and the compressor securely mounted on its shock absorbing rubber feet.

 Some compressors will be too tall for a standard lid, but will fit easily under the hi-top lids available for most ammo-type boxes sold in camping shops. 

We supply the control unit and the mobile phone app that drives it. You assemble the combo to your own requirements. In special cases we can supply the entire assembly as shown on the right.


The App 

The Mobile App
The Mobile App
Manual Control Buttons

In Manual Mode there are no pressure or time limits. The compressor and deflator both stay active as long as commanded. 

You can start the compressor by tapping the left-hand green button. The button turns red and you stop the compressor by tapping it.

You can open the deflator valve by tapping the right-hand green button. The button turns red and you can close the deflator by tapping it. The deflator icon will show a red border whenever to hose pressure falls below 100kPa to warn of unusably low tyre pressure.

Tyre Pressure Indicator

The controller measures hose pressure very accurately, but hose pressure will not be the same as tyre pressure during either inflation or deflation. To measure tyre pressure accurately the both the compressor and deflator must be OFF for at least 5 seconds to allow the pressure in the tyre to equalise with the hose pressure.

Compressor Power Switch

The controller switches 12V current to the compressor through power relays with a 60A capacity. The compressor has its own power switch which is effectively wired in series with the controller relay contacts, which is why the compressor's power switch must always be left in the ON position when the compressor is under remote control. If it is left OFF the controller will not be able to run the compressor. 

The controller has two Anderson SB50 plugs through which 12V power is carried to and from the controller. Either plug can be an input and either plug can be an output. The controller taps off a little bit of this power for its own use from whichever plug happens to be connected to the battery. The negative pole of the battery is permanently connected between the plugs while the positive pole gets switched through the power relays.

The Deflator Valve

The controller contains a small but powerful solenoid valve that can be opened electrically to facilitate deflation. Being a compact device in a confined space it will heat up after being energised for a time. Air being released from the air hose will serve to keep the solenoid cool indefinitely, but the solenoid should not be kept manually energised for prolonged periods when no air is flowing through it.

Auto Modes

During both inflation and deflation of the tyre the hose pressure (which is the pressure that the control unit is able to monitor) does not reflect the air pressure inside the tyre. This is because of the pressure difference on either side of the constriction of the tyre valve. To inflate or deflate automatically the system must make an educated guess at the time required to reach the target pressure and act accordingly.  If the first attempt does not reach the desired pressure additional attempts must be made.

The above mentioned educated guess, which as based  on:

  • The current pressure,
  • The target pressure,
  • The tyre size (1 of 5 to choose from),
  • The compressor size (1 of 5 to choose from),

can be made either by the control unit or by the mobile app. The default calculator is the one in the mobile app, but the controller can be selected to perform this function as well by pressing the word "Target" on the screen for at least 5 seconds. The phone will vibrate for a full second and the lock icon at top left will disappear. To return the calculation function to the mobile app simply restart the app.

If the controller is given the job of estimating the length of the inflate/deflate cycle the command to do so is given by tapping the middle green button on the mobile's screen. The controller will continue to initiate timed inflate and/or deflate cycles until either the target pressure is reached (+ or - 5mB), the activity is stopped by tapping the middle red button, or the mobile app is terminated.

If the default calculator in the mobile app is accepted there are 2 available modes of communication between the mobile and the control unit - Secure Mode and Free Mode, and the selection is made by double tapping the LOCK icon at top left. When the icon is shown as locked the Bluetooth communication link between the mobile phone and the control unit is supervised - if the phone goes out of range the compressor and deflator valve will both switch off.

If the LOCK icon is UN-locked the Bluetooth link is not supervised and the phone is allowed to go out of range. While out of range it will not be able to command either the compressor or deflator valve - they will both maintain the current operation until the time interval commanded from the phone expires. Communications will automatically restore when the mobile comes back into radio range, but the function of the app may have been changed in the meantime.

Timing Table
Timing Table

Whether control is seated in the mobile app or the control unit, the procedure is the same: The difference in pressure between what exists and what is desired is determined and a basic time span is calculated, the tyre size is used to modify this figure and further adjustments are made to compensate for high or low scale operations. If this is an inflation phase then the size of the compressor is also taken into account.

The Tyre Size slider control can be set to 5 tyre sizes: Very Small, Small, Medium, Large, and X-Large. Each increment in Tyre Size category will produce approximately 30% more inflation/deflation time than the previous category.

Because there are a wide variety of compressors on the market 1 of 5 compressor size categories can be selected. This covers a range of compressor capacities from 30 LPM for V-Small to approximately 170 LPM for X-Large. To select a compressor size double tap the Compressor icon. The slide control label will indicate "Compressor Size". Select between V-Small, Small, Medium, Large, and X-Large. The category that best fits your compressor will be found by trial and error. To Save tap the Compressor icon again. While in Compressor Size select Mode the other buttons are disabled. Once the correct size category for the compressor has been found this setup need never be changed again. With this wide range of variables it is possible that a tyre may fall into two different categories when being inflated or deflated.

At right is a table showing the running times in seconds for inflating as well as deflating between100kPa and 220kPa, as well as the same from 100kPa and 350kPa.

In the most-likely inflation scenario the tyre has been previously deflated to around 100kPa and must be re-inflated to about 220kPa. Ideally the compressor should be engaged for a slightly shorter time to achieve this objective, since another inflation phase will be initiated by the controller if the previous one did not reach target pressure. Especially it should not be engaged for longer since this will result in overshooting the target and require a deflation cycle, which will waste time and resources.

The actual inflation time required depends on the capacity of the compressor, which can vary widely, and the power available from the battery driving the compressor, (which may or may not be assisted by input from the alternator). Similarly the deflation time depends on the aperture offered by the tyre valve (which can vary from wheel to wheel). Consequently the best slider position for any given situation is something only learned by experience.

When Tyre Size is set to Minimum the inflation rate with a 160L compressor driven by a battery not being charged is timed to agree with a 15" x 235 tyre. Anything smaller will cause the pressure to overshoot and require a deflation phase. The deflator timing is intentionally set to initiate shorter cycle times so as not to overshoot the target pressure on the way down (which would require another inflation phase to correct).
The estimated time remaining is shown on the screen. 

Manual Mode
Manual Mode

When the estimated time has elapsed the controller stops inflation/deflation for 5 seconds and then reads the hose pressure. If the hose pressure is within 5 kPa of the Target Pressure it terminates Auto Mode and beeps. If the difference between hose pressure and Target Pressure is greater than 5 kPa it recalculates and starts another cycle. This repeats until hose pressure, and hence tyre pressure is within 5kPa of Target Pressure.
Setting the Tyre Size slider to too great a size will result in inflation or deflation overshooting Target Pressure and extra, avoidable cycles being required to reach the target. 

So always err the slider on the low side - start small, grow bigger.

Tapping the central red button terminates Auto Mode. If the App is terminated both the compressor and deflator are turned OFF.
Battery voltage is by the control unit and displayed on the screen. Low voltage (< 11.7V) is indicated by a RED background.
The flashlight button is provided for night-time work.

Failsafe Comms Mode (Locked or Unlocked Mode)

As can be seen on the inflate/deflate timings table above, a small compressor may be expected to take a considerable time to inflate a large tyre. At these times one may want to wander off and attend to some other matters. If this wandering takes the mobile phone out of Bluetooth range of the control unit, how is the controller to react? Should it keep on doing the inflate or deflate phase that it is busy with, until the mobile comes back into range and can resume control? (Unlocked Mode) Or should it stop its operation as soon as the Bluetooth connection is broken? (Locked Mode).

 By selecting Failsafe Mode you will force the controller to cease any operation whenever the mobile phone loses Bluetooth contact with the controller. By deselecting Failsafe Mode you ae instructing the controller to complete whatever operation it was engaged in immediately before the loss of communications with the mobile phone.

To engage Failsafe Mode double tap the lock icon at top left so that the lock appears secure. To open the lock double tap it again. The open lock icon indicates that the controller will continue the current operation despite loss of connection with the mobile phone.

Any runaway condition that might arise while the phone is out of contact with the controller is unlikely to have serious consequences. The tyre may be deflated completely if the deflator failed to switch off, or the tyre might be inflated to the point that the safety valve on the compressor opens. To remedy any such condition the controller ca simply be switched off while the Bluetooth link is re-established.

MAC Address

The mobile phone needs to be informed of the MAC Address of the controller with which it must communicate via Bluetooth. To accomplish this easy task make sure the mobile phone is Bluetooth connected (the blue rune will show at top left) and double-tap the App Title at the top of the screen. The current MAC Address will be displayed. Edit the 6 character pairs to that shown on the product sticker, and tap the App Title once more to Save. 

More detail can be found here: Set MAC Address where the Caravan Pilot procedure is described.

Power Considerations 

Manual Mode
Manual Mode

If you are using a compressor with some muscle - not one of those toys that plug into a cigarette lighter outlet and that get zipped into a little bag and kept under the seat, you'll be connecting directly onto the battery with at least an Anderson SB50 connector. Most people would want to keep the engine running at idle to prevent unnecessary discharge of the battery while operating the compressor. The control unit can switch a DC current of up to 60A though the the Anderson connectors employed are only rated for 50A, which is current the limit of compressors that we support. Few 160L compressors draw more than 45A Max.
Under these circumstances there should not be enough volt-drop to the compressor to affect the operation of the remote control unit. If Bluetooth communication should fail while the compressor is drawing power it points to a connection problem that undoubtedly also inhibits proper functioning of the compressor and requires urgent investigation.
The cable between battery and compressor should have a cross-section of 6mm², which can carry a current of up to 56A and be limited to about 2 metres if possible. Spring-loaded clamps are not ideal for connecting to a battery - it's advisable to make a short tail of 6sq/mm wires connected securely and permanently to the battery at one end and a Anderson SB50 plug at the other.
The controller monitors the battery voltage as it is found supplied to the controller and transmits this value to the mobile phone, where it is displayed on the screen. Because small changes in battery voltage can be very significant in indicating battery condition it is important to get an accurate value reported. Since component tolerances can vary from unit to unit there is a calibration facility built into the mobile phone app to equalise these variances.. 
To enter Voltage Calibration Mode hold the blue Bluetooth icon (top left) down and tap CaravanPilot logo (screen bottom) once. The Tyre Size slider now becomes the means to adjust the reported voltage. Move the slider in small increments, and allow several seconds for the display to stabilise after each adjustment, until it matches a trusted voltage reference such as a digital multi-meter.. To Save and Exit tap the CaravanPilot logo again and the display will revert to normal. 

Auto Mode
Auto Mode

As a benchmark value: we know that the voltage output of a healthy fully-charged battery after an hour at rest with no load will be 12,6V. As the battery ages this value will decrease through 12,5V 12,4V until at 12,3V the battery can be considered end-of-life since it's capacity is half of it's nominal value.
While discharging the output voltage of the battery will steadily decrease until, when about 90% of the available charge has been depleted, the voltage falls to the critical level of 11,7V. Most people do not want their battery voltage to drop below 11,7V because this is where the real damage occurs. Hard lead sulphate builds up on the surface of the plates and this permanently compromises battery capacity. Batteries can be ruined in a single deep-discharge event. To warn of excessive discharge the Voltage display will show a RED background when the measured voltage dips below 11,7V. Due to the internal resistance of the battery the output voltage does not accurately reflect it's state of charge while it is being discharged (or charged). Therefore only measurements made after the battery has at rest for several minutes (ideally up to an hour) are relevant .

Battery Terminal Clamps

Battery terminal clamps on the end of the power cable make it easy to quickly connect to any vehicle's battery, which is an advantage. The accompanying disadvantage is that intermittent short contacts are made which may involve some sparking.  The control unit is driven by a microcomputer that requires a steady power supply for reliable operation and is vulnerable to damage should the input power fluctuations overcome the very robust voltage regulation measures inside the control unit. Using battery clamps increases the possibility of control unit malfunction and should only be used in dire necessity, and then the battery clamps should be carefully attached to achieve the greatest possible contact area while the control unit is switched OFF.

Calibrating the Pressure Sensor to Ambient Pressure

On first use the internal pressure sensor baseline needs to be established. This is always done at manufacture but may in very rare circumstances need to be redone. (Such as when the controller firmware is upgraded and the memory is erased.)

With the hose input unconnected and open to the ambient pressure, hold down the Bluetooth icon at top left (the controller must be online) and then press the blue Hose Pressure indicator button until the phone buzzes briefly (this will take a second or less).  A command to zero the pressure sensor will be sent to the controller, and a toast popup message will indicate that the pressure sensor has been calibrated. No further action is required.

There is no need to adjust anything when transitioning from sea level to any other altitude since the pressure sensor measures absolute and not relative pressure.

Ammeter Option

Ammeter Showing Compressor Current
Ammeter Showing Compressor Current

The system can incorporate a sensitive ammeter to quantify and display the current drawn by the compressor. The ammeter module also offers a sensitive and highly accurate voltmeter for monitoring the voltage supplied to the compressor. This replaces the standard generic voltmeter which is otherwise provided.









First Use of Flashlight

Android requires the user to grant access permission to the app to use the flashlight. On later versions of Android this permission lapses after a period of time if the flashlight is not used and permission will again have to be granted. The app will be moved to the background by Android while this takes place and you will have to bring it forward again manually.





Building Your Own Assembly 

Ammo Box Layout
Ammo Box Layout

Step one: start with a respectable compressor. There is a very capable Chinese-built unit that is rated at 160 litres per minute and is sold by supermarkets, motor spares outlets, camping warehouses, and 4x4 shops at a price that ranges from R1800 to well over R3000. With this compressor you can reliably inflate 6 large tyres without cooking the pump. 

Next, you need rubber hose. That spiral plastic pipe supplied with many versions of this compressor is a huge annoyance and can severely damage your tyre valve by pulling it against a spiral pipe that is too short for the job. If the valve body tears where it passes through the rim you need to unmount the tyre to replace it, which is a huge challenge at the roadside. The hose should have ample length to reach the furthest wheel.

Hinged Lid
Hinged Lid

Then you need a box to house the kit. There's a cheapish version of ammo box that is sold by Makro and various camping shops. If you have the popular 160L compressor you'll need a high-top lid on the ammo box or the lid won't close.

If you want to coil the hose under the lid you'll want to hinge the lid to the box. For this you need two pieces brass piano hinge, some pop rivets, and some spacer material to go under the lower half of the hinge. Be sure to mount the hinges so the lid can open some distance past vertical. To accommodate the pop rivets you'll need to drill counter holes under the hinges rather than put the rivets in backwards. Use a piece of nylon rope to limit the lid's travel past vertical so it won't break  the hinges.

If your compressor comes with a mounting plate that stands on rubber feet, you can remove it from the plate and mount the compressor directly on the floor of the ammo box using the original rubber shock mounts. Leave a bit of an air gap all around the compressor's cylinder cooling fins but remember the bend in the hose needed at the other end, so a compromise is called for.

Hose Coiler
Hose Coiler

If you use our PneuMatic control unit, mount this in the corner of the box that is convenient to the compressor's cylinder and compatible with hose bends required to reach it. Mount it high enough that you can pull the Anderson SB50 plugs easily, but no so high that the Anderson plugs interfere with the lid. Use stainless steel M8 fasteners with spring washers so you need to make the bolts too tight. You need to be able to pull both plugs from the control unit and couple them to each other in the event of the mobile phone not being available. The quick-disconnect coupling should also be easily accessible for the same reason.

You'll need a T-piece in the hose coming out of the compressor to connect to the quick-disconnect coupling on the control unit. The original mechanical gauge should be incorporated into the hose at some point to constitute a backup system should the electronic system be unavailable for any reason. The T-piece is a good place to mount the mechanical gauge but it will need soldering. Reuse the screw-on valve connector from the original hose or pipe.

You can then make a coiling frame to bolt to the underside of the lid with arms long enough to coil 10 metres of hose. Remember to place this where it won't interfere with the compressor. Take the original rubber feet off the compressor's mounting plate and attach them to the underside of the ammo box.

The spring clamps that the compressor comes with are not suited to any particular purpose and should be discarded. Remember that a motor that receives a low voltage will draw a higher current and will heat up much quicker than one receiving full power, and the clamps are guaranteed to make a poor connection. 

Pressure Gauge
Pressure Gauge

Consider mounting an Anderson SB50 plug on the exterior of the vehicle near the battery where it can be accessed easily, and wire this direct to the battery with 6mm² wire. Protect this wire against damage and add an inline fuse if necessary. The best way to solder the Anderson terminals is to:

  1. clamp the terminal in a vise with the cup facing upwards and the lip oriented correctly for the plug body,
  2. heat the terminal with a mini butane blow torch such as you get in camping shops,
  3. half fill the heated terminal with solder,
  4. and then plunge the stripped end of the wire into the half-filled cup of the terminal.
  5. Remove the heat source and wait a few seconds for the solder to solidify convincingly.

Attach a sticker warning against closing the box while the compressor is hot. 

Warning Label
Warning Label

There should still be lots of room in the box for patches tyre levers and other accessories. 







The controller is a rugged and reliable device which has proven itself over many years of service. However it is a complex device and requires the presence of a working mobile phone, so failures are always possible.

If the controller will not connect via Bluetooth there may be MAC address or pairing issues. Set MAC Address has more info on this.

Both the power relays and the deflator valve make an audible click when energised. If the manual Compressor button on the mobile is pressed and a click is heard this means the relays are energised. If the compressor motor does not start it is because the compressor is switched OFF or the thermal protection has tripped. Many compressors have a thermal cut-out switch that interrupts the current when it gets hot, and recloses when the heat dissipates, or may required manual reset. Bypassing the controller will bring this to light.

The contact points in an Anderson SB50 plug are normally held in place by spring-loaded metal blades. Under some circumstances, such as when excess solder contaminates the outer surface of these contacts or there is a mismatch between plug body and contact manufactures, the contact element is able to partially back out of the plug housing, a condition that is easily spotted in a visual inspection, and should be properly taken care of since it is likely to recur.

If the manual Deflate button is pressed and a click is heard but no air flows there is a blockage somewhere. Blowing into the hose coupling will tell you whether it is in the controller or not. Remove the controller from the ammo box (6mm Allen key and 13mm AF spanner), remove the 4 Phillips machine screws (No 0 Phillips), and carefully separate the controller's lid (there are wires joining the 2 halves). With a jeweller's Phillips remove the 2 screws holding the white nylon moulding to the metal frame and move it aside without removing the plastic pipe. There is a spring-loaded plunger that will try to escape. Remove the particle of debris and reassemble in the reverse order. Be sure that the plastic tubing through the lid covers the valve outlet.

To operate the compressor without the controller detach the 2 Anderson SB50 plugs from the controller and connect them to  each other - the polarities will always be correct. The hose should always be fitted with a mechanical pressure gauge, and a foot pump kept as final backup. 

The deflator valve may fail to close if some debris from the hose or tyre gets jammed in it. Uncouple the air hose from the controller - the coupler is self-sealing. The deflator valve can be opened with the aid of a jewellers Phillips screwdriver and cleaned out. The process takes about 10 minutes and requires no special skills.

 Summary of User Setups:

MAC Address 

Double tap Heading line. Edit MAC. Tap Heading again

Tyre Size

Move anytime to 1 of 5 sizes. Effective on next cycle. This affects both Inflate and Deflate times in Auto Mode only.

Compressor Size

Double tap compressor icon when three green buttons are showing (idle mode). Select 1 of 5 sizes. Tap icon again to save. Effective on next cycle. Other buttons inactive while this is busy. This affects only Inflate times in Auto Mode only.

Battery Voltage

Press Bluetooth rune while tapping CaravanPilot logo once. Move slider slowly until voltage matches trusted voltmeter. Tap logo again to Save. Must be online.

Target Pressure

Tap UP or DOWN arrows anytime. Effective on next cycle. Range is 100kPa to 350kPa.

Zero Pressure Sensor

Not normally required. With hose open to the atmosphere hold Bluetooth rune and press blue Pressure Display button. After half a second phone will buzz and toast message will appear. Must be online.