European Tour – Hopefully!

I am planning on launching from Cambridge on Saturday the 13th of April 2013. With updated code and a map of where APRS in the air is permitted the payload being flow will include the APRS transmitter :

IMG_1211With a pack of 6 x AA batteries (3.6V out seen in pink gaffer in the background ) the payload should have about a weeks power possibly longer.

Assembled in a hollow polystyrene ball with antennas for 70cms (1/4 wave) and 2 meters ( Slim Jim suspended underneth the payload) comes in at fairly portly (for me) 180g :


This will be suspended under a 1600g Hwoyee balloon filled with H2 for an ascent rate of about 1.5m/s. Watch from about 10am on Saturday :


To France! and back!

Dave Akerman kindly offered to launch a MAX7C based board for testing last weekend. I prepared the PCB and posted it out to Dave who sent it up under a 1600g Hwoyee with a slowish ascent rate. The plan was for a float but the balloon unfortunately burst rather than entered into a float.

It did however make it to France (just) :


it appeared the parachute tangled badly and it “landed” in a field at 15.9m/s (44mph) :

IMG_0883The impact although significant (it broke the battery off the board and bent the ICSP connector in the process) the transmitter continued operating. F5APQ kindly located the payload in a frosty field very early the next morning still transmitting :


Jacques kindly untangled the mess and returned the payload to me back in the UK ready to fly again :


So a massive thanks to F5APQ to going out of his way to do that.

Technically the uBLOX MAX7C performed as expected with no blips, the APRS Geofence correctly identified when it crossed into France, shame the balloon didn’t float but a good result in the end!

Ublox MAX7C

EDIT2 : These are now in stock and available at HAB Supplies

EDIT : The extremely long long times were very odd and I’m not sure something environmental wasn’t going on. I’ve subsequently tested both modules repeatedly and from cold inside (in a window) they are getting 3D locks from cold in sub 40 seconds consistently.

Finally the long awaited sample of the new offering from uBlox landed on my desk. The MAX-7C is the latest module from uBlox offering better power usage and performance. Additionally the MAX-7C can run from 1.65v to 3.6v meaning it can be used on both 1.8v and 3.3v boards with no problems. Additionally the UAV/RC crowd will love the 10Hz updates.

Downsides ? No more TCXO meaning lock times may be slower. I set up a testing environment mounting the MAX7 on a breakout with a chip antenna :


Along side was a MAX6Q for comparison. Firstly I ran the MAX6Q noting the power usage from 3.3v :

Aquiring 60mA (Average over 5 mins no lock)
Tracking 44mA (Average over 20 mins)
Cyclic      15mA (Average over 15 mins)

Its worth noting the GPS did seem to take an extremely long time to lock that evening, normally its nothing like 5 mins.

Now the MAX7 :

Aquiring 22mA (Average over 20 mins no lock)
Tracking 17mA (Average over 10 mins)
Cyclic    6mA (Average over 10 mins)

Conclusion : In the very brief test I did the MAX7 did take longer to get a lock than the MAX6, however once it was locked the performance was very similar, I couldn’t tell any difference. However the big difference is the power usage. Reducing the usage in cyclic by over 50% is a massive improvement. I can’t wait to run test one of these on a the PAVA boards.

Additionally I tested 10Hz mode which seems to be pretty good, however further testing is needed. Once I’m confident with it I’ll have these for sale on

Launch! Pico time!

When I sat down and designed the PAVA PCB I had in mind launching this under a small foil balloon. These are interesting for a number of reasons, firstly you don’t need a NOTAM, secondly under the right conditions they can float. Although alot of these foil pico launches have been done by members of the UKHAS community I decided it was time for me to do one.

Armed with some 36″ Qualatex balloons from Random Engineering I set about making a very small and light payload based on a single AA and the PAVA R7 PCB :

IMG_1061Coming in at 27g the antennas were made from the inside of CAT5 cables. The case was made from a hollowed out piece of insulation with additional thin insulation in close contact with the PCB. See here for further build images :

To fill the balloon I used a piece of thin tube. I’d been advised to aim for a neck lift of about 1g, to measure this I had a piece of blutac 1g heavier than the payload. I was suprised how quickly the balloon filled up and it may have been slightly over filled :


Launch was extremely windy :

I was happy to see it go as it was pulling towards the ground. Once in the air it floated up gently with an average ascent of about 1-1.5 m/s. Now in theory these things should float at about 4500m but PAVA didn’t it carried on upwards unfortunately too high for the balloon to remain intact. All of a sudden PAVA started to fall at an alarming rate.

Normally with Pico’s they are so light the balloon acts like a streamer slowing down the decent, however there was nothing slow with the 12m/s it hit the ground at. Fortunately it appeared to land in a field. About an hour later we started getting telemetry from the payload again, it seemed one of the people who had been tracking, 2E0KPI had decided to and have a look for it.

Despite the dramatic decent PAVA was still transmitting, however with fading light 2E0KPI was unable to locate the payload. He kindly agreed to go back the next day and have another look where he located PAVA, still transmitting, in a field. The reason for the descent rate was clear, the balloon had blown its valve entirely out :

03032013133A big thanks to 2E0KPI for locating the payload and to all the trackers. I’ll have another go at this soon. Congratulations to James Coxon M6JCX who launched an ATLAS/PAVA board around the same time. In a good demonstration on how to do it his balloon went on a 34 hour jaunt around the UK !

Launch ! (Sans APRS)

Dave Akerman kindly invited me along to launch on Wednesday the 27th of Feb. Dave was launching a Raspberry Pi powered Tardis and has a great write up >here<. Due to the lack of time to ascertain the legality of transmitting APRS in the air I took the decisions not to fly the ATLAS/PAVA board. Instead I ran the same code on my standard PAVA board. It wouldn’t transmit APRS (wasn’t a transmitter fitted) but it would transmit the current ITU country code via RTTY and should be a good test of the code if nothing else.

Dave kindly fabricated a polystyrene ball container and antenna whilst I was driving down and still managed to find time to paint it fluorescent pink (Thanks Dave! Here on the left shown next to PAVA the backup tracker for the Pi launch on the right) :


We decided to get the floater up first. To get the latex balloons to float you need to fill the balloon such that you get an extremely slow ascent rate, normally its suggested you aim for about 5.5m/s however to float we aim for less than 4.5m/s. In the end we decided to aim for 2m/s, which is a compromise between time taken to ascend and chance of floating.

With the Hwoyee 1600g balloon with H2 and the 65g payload this equated to about 320g of neck lift. This was a problem as the filler and hose weighed 550g. In the end we removed the filler and hung some gaffer tape rolls on the balloon, so the neck lift was about right. Attaching the pink ball the launch was quite calm and the balloon floated off upwards bang on target ascent rate :

IMG_1472At this point Dave and I concentrated on the Pi launch which I won’t cover too much here as Dave covers it in his blog. We occasionally glanced at and the ascent rate was on track and AVA was heading out over the Bristol Channel as expected.

Our concentration taken by the Pi launch we didn’t noticed AVA creeping upwards slowly, it spend alot of time out over the Bristol Channel as it slowly turned direction. Sucessfully recovering the Pi from a field we directed our attention to AVA which was now tracking east towards London and the quite incredible speed of 110mph.

In the hour it took us to get back from the Pi landing site to Daves AVA had left mainland UK and was heading out over the channel at an altitude of 38.5km (126,000 feet) maintaining its extremely fast pace at times touching 120mph. A small (but critical) error in the code exhibited itself at this point, it seems the Geofence for the UK isn’t correct and had the payload had an APRS transmitter it would have started to transmit just east of London which would have been bad!

Hoping the rest of the Geofences would work I headed back to Yorkshire, Dave soon called me to advise as AVA had skimmed French airspace the ITU prefix switch to F, followed shortly by ON as it entered Belgium. Success! As it crossed the Netherlands this switched to PA and then to DL as it entered German airspace at 17:13.

As the sun set AVA was careering across Germany maintaining a corking speed, sadly at 17:51 the radio transmitted its last full sentence, shortly afterwards the radio stopped. This is a known issue with the RFM22B’s and is usually related to them getting cold. I have modified the code to power cycle the radio every 50 lines.

From the point where it turned over Weston Super Mare to the last received packet it managed to go 753km at an average speed of 167kmph, just over 100mph :


Many thanks to Dave Akerman for helping with the launch and providing the gas and to all the receivers who take the time to listen out for these payloads.

Images from the day here :

Daves blog about the day :

APRS Floater Launch is Go… or not

Having completed the code for the APRS/RTTY Payload I got round to making a container and an antenna for it. The 70cms antenna was just going to be the normal 1/4 wave however the 2 meter one had to be slightly different. I settled on a Slim Jim made from twin core feeder wire. Using M0UKD’s Slim Jim Calculator I quickly made one up and made a choke out of some 40mm PVC tubing.

The estimates for battery life were a whopping 70 hours for each pair of AA’s in the payload (The operating battery voltage had to be > 3V or the efficiencies on the 5V stepup started to cause issues). In the end I decided on 3 pairs of AA energizers. Enough for continuous TX for about a week.


Here you can see the battery pack on the left and the transmitters on the right.
IMG_1143All fastened up note slim jim hanging below. Full build pics >here<

It was all ready to go, just plug in and launch then a spanner in the works. Apparently the operation of amateur radio equipment in the air isn’t permitted in France. Maybe. With the situation becoming unclear and the launch window rapidly approaching I made the decision not to launch the payload. Instead we’d launch a PAVA board with the same code on to test the Geofencing.

Preparing for a European Floater

A floater is a balloon that reaches a certain height then doesn’t burst and continues to float at a given altitude. In practice the only balloon that can do this reliably is the Hwoyee 1600g with a slow ascent rate and the smaller foil balloons.

This was demonstrated to great effect (and accidentally!) by Apex Alpha‘s epic flight to Europe. Unfortunately Apex Alpha left the range of the tracking network and was never seen again. Our tracking network has expanded dramatically since then and thanks to SP9UOB’s efforts the number of stations in Poland (where Apex Alpha was lost) means we should have great coverage out there.

However the tracking network is an active thing, people need to be actively listening out for the payload. There is an alternative which is used alot in the US but not in the UK due to our laws. The APRS (Automated Packet Reporting System) is “an amateur radio-based system for real time tactical digital communications of information of immediate value in the local area“.

Its a passive network meaning if you transmit on this and there is a station listening in the area your packet will be digirepeated and you will get your location on the map. Unlike the RTTY based system this is all automatic and needs no one to retune or run custom software. Unfortunately although a network of APRS stations exists in the UK the use of Amateur Radio in any “Aircraft or other Airborne Vehicle” is forbidden. However there is away round this…

Inspired by Apex Alphas successful “failure” Project Swift planned to do this with a dual transmitter board, the Swift board although functional was heavy and needs alot of batteries. In conjunction with James Coxon (M6JCX) we planned a version of the PAVA board that allowed the connection of a separate daughter-board with a HX1 transmitter on it.

The board would have the usual stepup regulator on it, the HX1 requiring 5V would have a separate stepup on it which to save power could be powered on and off as needed. So the ATLAS/PAVA board was born :

IMG_1064On the left is the microcontroller board running at 1.8V (GPS and RFM22B transmitter on the bottom) and on the right is the HX1 Daughterboard for APRS. The HX1 TXD was fed by a NPN transistor to take the 0-1.8v up to 0-3v. Additionally the GPS was fitted with a PFET to allow the GPS to be turned off and on if needed.

The microcontroller board could be run on its own or with the HX1 transmitter clipped to the top. To ensure compliance with the law code would be written to “Geofence” europe into countries, this was done in Google Earth. Code was then borrowed from Project Swift to ascertain if the payload was currently within a certain area :


From here we can take action such as turning the APRS off entirely to comply with local legislation or amending the ITU prefix to comply with the CEPT regulations. I.e when in France the call sign of the balloon should be F/M0UPU.

This map above is availble as a KML here :

Once I worked out a number of faults with the original board one was shipped off to James for testing, I hope to launch one soon as well.

Remote Controlled Power Switch

With K3NG’s Rotator Control Software and my interface I am now able to remotely control my rotator so when there are launches in the day I can track them from work….if I remember to turn the rotator control unit on.

This seems to be the sticking point and I was constantly forgetting to power the control unit on before leaving for work. Therefore I decided to make a remote control power switch and link it into the rotator control unit. I ordered a 5V Relay Module from everyones favourite tat store

When it arrived a few weeks later I wired this into a butchered 4 way extension :

IMG_1104 IMG_1105After replacing the 13A fuses in the plug and 4 way with 3A ones (the relay is a chinese rated 10A), PAT tested it (passed!) I wired it up to a test Arduino to confirm it worked. The lead to the rotator controller was made from a head phone extension cut in two so it can be removed as needed. After soldering it to the Arduino 5V, GND and A4 pins I amended K3NG’s code as follows, changing all the “button” references to 0 (I don’t use the buttons).

#define IDLE_TIMEOUT 1 // Idle time out in mins

unsigned long idle_timer;

void loop() {

 if( (millis()-idle_timer) > (60000*IDLE_TIMEOUT) ) {
 digitalWrite(POWERSWITCH, LOW);
 digitalWrite(POWERSWITCH, HIGH);

 void check_serial(){

if (Serial.available() > 0) {
 if (serial_led) {
 digitalWrite(serial_led, HIGH); // blink the LED just to say we got something
 incoming_serial_byte =;

Now if there is no serial activity for 1 min the Arduino powers the controller off. Issue any serial command (i.e open PSTRotate) and it powers the controller on, and to boot turns the LCD back light on.

So now even if I do forget to turn the controller on I don’t have to revert to remote control V0.1 (“The Lovely Wife”)


Pico Payload

Although I’ve made smaller boards for a while now I’ve never done a Pico launch. Pico launch is generally a small, NOTAM exempt (< 2 meters diameter at any point) balloon. I’ve obtained some 36″ Qualatex Foil balloons from These can lift about 60g to about 4km and will, hopefully, float.

Taking the existing board and breaking out the hot wire cutter I set about making a very small but insulated container for the board out of expanded polystyrene :

IMG_1058The single AA was mounted centrally, a small piece of thin foam insulated this from the PCB which was placed on top. An external battery connector was installed and then the radials were added directly to the board made from CAT5 cable.

IMG_1060Finally the top was hot glued in place the result is 27g :

IMG_1062I hope to launch this next weekend but very subject to weather. Telemetry will contain the temperature as reported from the RFM22B’s internal sensor and a bit field for the status (last field) as follows :

Bit 0 = GPS Error Condition Noted Switch to Max Performance Mode 
Bit 1 = GPS Error Condition Noted Cold Boot GPS
Bit 2 = RFM22B Error Condition Noted, RFM22B Power Cycled 
Bit 3 = Current Dynamic Model 0 = Flight 1 = Pedestrian 
Bit 4 = PSM Status 0 = PSM On 1 = PSM Off  
Bit 5 = Lock 0 = GPS Locked 1= Not Locked

I.e status code 8 = Pedestrian mode.

PAVA R7 Further Power Saving

Due to a cock up with the design (I’d left copper pour under the GPS antenna so no lock) I had to get some more PCB’s made. Given how many of these seem to be ending in the sea and how you can’t see design cockups on black PCB’s I decided to go with plain old boring green for PAVA R7b. However they look quite nice :

2012-12-27 14.25.18

Specs as before with the small addition of a 1.8V LED for status reporting as needed.

Testing last week with the 3.3V board under the following conditions : continuous TX @ 11dB , input voltage 1.58v with no power saving code saw a average draw of 254mA from the battery. This equates to about 12 hours run time from a single AA. Implementing power saving code, turning off the ADC and putting the GPS in 1 second cyclic mode brought this down to 148mA increasing run time to about 20 hours from an AA.

Now the 1.8V boards are here I ran the same power saving code under the same conditions. The result is an average draw, once lock has been attained, of 66mA from the battery. This equates to theoretical 45 hour + run time from a single AA. It may be more as it seems to use less power the more satellites it has, this maybe offset against the temperature however. Look ma no power :IMG_1380As noted by James Coxon you can’t implement power saving mode until you have a lock. I also found engaging it before you had more than 5 satellites was problematic.

I was unable to get anything other than the default 1 second cyclic mode working. In fact amending the cyclic to anything other than default seemed to cause issues, the clock stopped counting and the module started behaving erratically. However just turning cyclic mode on with no other changes seems to work.

void setGPS_PowerSaveMode() {
 // Power Save Mode
 uint8_t setPSM[] = {
 0xB5, 0x62, 0x06, 0x11, 0x02, 0x00, 0x08, 0x01, 0x22, 0x92 }; // Setup for Power Save Mode (Default Cyclic 1s)
 sendUBX(setPSM, sizeof(setPSM)/sizeof(uint8_t));

The following code may be useful as well :

void setGps_MaxPerformanceMode() {
 //Set GPS for Max Performance Mode
 uint8_t setMax[] = {
 0xB5, 0x62, 0x06, 0x11, 0x02, 0x00, 0x08, 0x00, 0x21, 0x91 }; // Setup for Max Power Mode
 sendUBX(setMax, sizeof(setMax)/sizeof(uint8_t));
void resetGPS() { // Cold Boot GPS
 uint8_t set_reset[] = {
 0xB5, 0x62, 0x06, 0x04, 0x04, 0x00, 0xFF, 0x87, 0x00, 0x00, 0x94, 0xF5 };
 sendUBX(set_reset, sizeof(set_reset)/sizeof(uint8_t));