 testName = "Seek";
 testDescription = "Seek test performs " + QString::number(SEEKER_SEEKCOUNT) +
   " seeks to random positions on device." +
   " Seek lenght is marked on horizontal axis and seek duration is on vertical axis.";
}

Seeker::~Seeker() {}

void Seeker::TestLoop() {
 // erease previous results
 result.erase();
 
 // initialize random number generator
 RandomGenerator gen;
 
 // seek to drive end
 hddsize last = device->GetSize();
 device->SeekTo(last);
 
 // test SEEKER_SEEKCOUNT seeks
 for(int i = 0; i < SEEKER_SEEKCOUNT; ++i) {
  hddsize next = gen.Get64() % device->GetSize();	// get next position
  
  // make timed seek
  hddtime timediff = device->SeekTo(next);
  
  // count seek length
  uint64_t posdiff;
  if(last > next)
   posdiff = last - next;
  else
   posdiff = next - last;
  
  // set last position for next test
  last = next;
  
  qreal pos = (qreal)posdiff / (qreal)device->GetSize();	// calculate pos relative to drivesize
  qreal time = (qreal)timediff / 1000.0;			// evaluate seek time in miliseconds
  
  result.AddSeek(QPointF(pos, time));	// add seek to results
  
  // count test progress
  result.progress = i * 100 / (SEEKER_SEEKCOUNT - 1);
  
  if(testState == STOPPING) {
   return; 
}

void Seeker::InitScene() {
 // clear ticks
 dataTicks->erase();
}
void Seeker::UpdateScene() {
 // draw new seeks
 while(!result.newseeks.empty()) {
  QPointF seek = result.newseeks.pop();
  
  // mark seek as important if it is close to average
  if(seek.ry() < SEEKER_IMPORTANT * result.avg()) {
   dataTicks->AddTick(seek.y(), seek.x(), true);
  } else {
   dataTicks->AddTick(seek.y(), seek.x(), false);
  }
 }
 
 // draw new reference seeks
 while(!reference.newseeks.empty()) {
  QPointF seek = reference.newseeks.pop();
  
  // mark seek as important if it is close to average
  if(seek.ry() < SEEKER_IMPORTANT * reference.avg()) {
   referenceTicks->AddTick(seek.y(), seek.x(), true);
  } else {
   referenceTicks->AddTick(seek.y(), seek.x(), false);
  }
 }
 
 // update lines
 dataAvgLine->SetValue(result.avg());
 referenceAvgLine->SetValue(reference.avg());
 
 // rescale view
 Rescale();
}

int Seeker::GetProgress() {
 return result.progress;
}

void Seeker::SeekResult::AddSeek(QPointF seek) {
 // count new average seek
 average = ((qreal)seeks.count() * average + seek.y()) / (seeks.count() + 1);
 
 seeks.push_back(seek);		// add seek to result seek list
 newseeks.push_back(seek);	// add sekk to stack used for drawing new results
}

qreal Seeker::SeekResult::avg() {
 return average;
}

void Seeker::SeekResult::erase() {
 seeks.erase(seeks.begin(), seeks.end());
 newseeks.erase(newseeks.begin(), newseeks.end());
 progress = 0.0f;
 average = 0.0f;
}

QDomElement Seeker::WriteResults(QDomDocument &doc) {
 // create main seek element
 QDomElement master = doc.createElement("Seeker");
 master.setAttribute("valid", (GetProgress() == 100)?"yes":"no");
 doc.appendChild(master);
 
 // add values to main element
 if(GetProgress() == 100) for(int i = 0; i < result.seeks.size(); ++i) {
  QDomElement value = doc.createElement("Seek");
  value.setAttribute("length", result.seeks[i].x());
  value.setAttribute("time", result.seeks[i].y());
  master.appendChild(value);
 }
 
 return master;
}

void Seeker::RestoreResults(QDomElement &results, DataSet dataset) {
 SeekResult &result = (dataset == REFERENCE)?this->reference:this->result;
 
 // Locate main seek element
 QDomElement seek = results.firstChildElement("Seeker");
 if(!seek.attribute("valid", "no").compare("no")) {
  return;
 }
 
 // clear results and initialize scene
 result.erase();
 (dataset == REFERENCE)?referenceTicks->erase():dataTicks->erase();
 
 // get list of seeks
 QDomNodeList seeks = seek.elementsByTagName("Seek");
 
 // read result data
 for(int i = 0; i < seeks.size(); ++i) {
  result.AddSeek(
     QPointF(
      seeks.at(i).toElement().attribute("length", "0").toDouble(),
      seeks.at(i).toElement().attribute("time", "0").toDouble()));
 }
 
 // set progress
 result.progress = 100;
 
 // refresh view
 UpdateScene();
}

void Seeker::EraseResults(DataSet dataset) {
 if(dataset == RESULTS) {
  result.erase();
  dataTicks->erase();
 } else {
  reference.erase();
  referenceTicks->erase();
 }
 UpdateScene();
}

Solar charger

I was looking for some creative solution for powering my smartphone when being off the power grid. My phone ZTE Blade is quite power hungry. It can operate only for a few days even when used lightly. Actually it is not a problem to discharge it completely during one day. As I like going for long trips to nature I decided to build a solar charger.

Design

The phone has a charger that connects via a micro-USB connector. It can drain power from a AC charger or standard USB port (the AC charger is slightly faster). Standard USB port has 5 Volts and should provide current up to 0.5 Ampere. This means it has output of 2.5 Watts. I decided to buy a slightly more powerful solar panel with output power of 5 Watts. Unfortunately the solar panel has open circuit voltage of 21 Volts, so connecting it directly to phone would almost certainly broke the phone. To connect the panel to the phone I used a DC-DC changer. I tried to build a DC-DC changer myself, but it was not working properly. Even when it had good efficiency when powered from 12V battery it was not working well when connected to a solar cells. The overall efficiency at full daylight was somewhere around 30%. Finally I bought a DC-DC changer on Ebay and it works really great.

Hardware

Solar panel

Product: Rich Solar RS-M5 5Wp
Technology: Monocrystalline
Maximum output power: 5 Watts
Maximum power voltage: 17.82 Volts
Maximum power current: 0.29 Ampere
Weight 1.2 Kg

DC-DC power module

Product: NO-name from Ebay
Input voltage: 7-24 Volts
Output voltage: 5 Volts
Output current: 2.5 Ampere
Efficiency: 96% (highest really measured was 92%)

How does it charge the phone

After connecting the panel and the changer together I decided to test the output power. I tried to measure the absolute output power at 5 Volts and the conversion efficiency of the DC-DC converter. The first test was at the broad daylight (no clouds) with panel directed at the sun. The maximum current at 5 Volts (before the voltage dropped below 4.9 Volts) was somewhere around 0.8 Ampere. The conversion efficiency was around 85%. Under the suboptimal conditions (some clouds, panel laying at ground), but still on the summer sunshine the output was still good. Output power at 5 Volts dropped to 0.5 Ampere with almost the same conversion efficiency. When there are too many clouds (the shadows start to disappear) the conversion efficiency drops to 70% and the current is somewhere around 0.15 Ampere at 5 Volts.

The phone drains 0.38 Ampere from the USB so it can charge at full speed even when the conditions are not optimal. Unfortunately when the current drops it never comes back until the phone is reconnected. So when the panel gets to the shadow for a few moments the phone continue to charge at reduced speed until disconnected and connected again.

Conclusions

Once I proved that the thing will work I customized the solar panel body. The panel itself is installed in a frame from aluminum alloy. I installed the DC-DC converter inside the frame. In order to get the phone easily connected I drilled a hole in the frame and installed a USB header from PC case in it. Moreover I drilled four more holes in the frame and installed flexible straps in them. The straps help to mount the panel on the backpack.

Plans to the future

The solar charger is working good enough to satisfy my expectations. It is build from quite cheap components and works reliably. Unfortunately it is quite heavy. Now I am searching the web for amorphous solar panel. These are more expensive but can be bended. This means the cells itself do not have to be in solid metal frame covered with glass. The 5 Watt cells covered with thin plastic film can weight only 150 grams. Moreover the amorphous panels have better efficiency when on indirect sunlight.

To make matters worse I have to make up something for winter trips...