# Basic electron serial reading fails, works on photon

**URL:** <https://community.particle.io/t/basic-electron-serial-reading-fails-works-on-photon/22021>\
**Category:** Troubleshooting\
**Created:** [April 12, 2016, 2:39am UTC](https://community.particle.io/t/basic-electron-serial-reading-fails-works-on-photon/22021 "2016-04-12T02:39:45Z")\
**Posts on this page:** 5\
**Page:** 1

<div class="post-metadata">

**Author:** ![tedder](https://sea2.discourse-cdn.com/flex026/user_avatar/community.particle.io/tedder/32/9646_2.png) [@tedder](https://community.particle.io/u/tedder)\
**Post date:** [April 12, 2016, 2:39am UTC](https://community.particle.io/t/basic-electron-serial-reading-fails-works-on-photon/22021/1 "2016-04-12T02:39:45Z")

</div>

Is there a known problem with the Electron and reading serial?

I’m using a really basic sketch to read off of [a GPS device](https://www.sparkfun.com/products/13740). I simplified it to a test to probe that there are problems on the Electron. I’m running this sketch on a Photon (it works) and the Electron (and it fails as seen). It looks almost like there are missing characters.

Output from Electron (running 0.4.8):

```
35N166,G11,,*V034,,7,,1,7,
45,,75
,4314L8.0A$GPRMC,023506.00,A,4531.97180,N,12241.94173,W,1.271
T,KP0.23.M,S,0,8
43,,03
260790$,,,802G14,5

```

Output from Photon (running 0.4.9):

```
$GPGSV,4,3,15,24,58,259,26,25,07,295,,28,15,105,26,32,05,330,*7F

$GPGSV,4,4,15,46,34,146,,48,37,194,,51,35,159,*40

$GPGLL,4531.96822,N,12241.94001,W,022932.00,A,A*7F

```

And here’s the code:

```
void setup()
{
  Serial.begin(115200);
  Serial1.begin(9600);
  delay(1000*5);

}

void loop()
{
    if (Serial1.available() ) {
        char c = Serial1.read();
        if (c == 10 || c == 13) {
            Serial.println();
        } else {
            Serial.write(c);
        }
    }
    
}
```

---

<div class="post-metadata">

**Author:** ![tedder](https://sea2.discourse-cdn.com/flex026/user_avatar/community.particle.io/tedder/32/9646_2.png) [@tedder](https://community.particle.io/u/tedder)\
**Post date:** [April 12, 2016, 2:55am UTC](https://community.particle.io/t/basic-electron-serial-reading-fails-works-on-photon/22021/2 "2016-04-12T02:55:28Z")

</div>

Going with the theory that printing was too slow, I changed the code to fast-buffer (borrowing some of the Tracker code). Still failing.

Sample output:

```
$GPRMC,025403.00,A,4531.97434,N,12241.94374,W,0.902*G96
25N44.,G6,44G,1,,,,$2,91,9G13,5,4,,,9G92W0
$GPRMC,025404.00,A,4531.97396,N,12241.94273,W,0.581
T4KP0.13.M,A0,3
44,,1,D4,7152
,1,2,,G,,,$3,707$GPRMC,025405.00,A,4531.97381,N,12241.94282,W,0.4391

```

Code:

```
#define MAX_LINE_LENGTH 160
int lineidx = 0;
char currentLine[MAX_LINE_LENGTH];

void setup()
{
  Serial.begin(115200);
  Serial1.begin(9600);
  delay(1000*5);

}

void loop()
{

    if (Serial1.available() ) {
        char c = Serial1.read();
        if (c == '\r' || c == '\n') {
            Serial.println(currentLine);
            currentLine[0] = 0;
            lineidx = 0;
        } else {
            currentLine[lineidx++] = c;
            currentLine[lineidx] = 0;
        }
    }
    
    if (lineidx - 2 > MAX_LINE_LENGTH) {
        Serial.println("string too long, resetting.");
        currentLine[0] = 0;
        lineidx = 0;
    } 
    
}
```

---

<div class="post-metadata">

**Author:** ![tedder](https://sea2.discourse-cdn.com/flex026/user_avatar/community.particle.io/tedder/32/9646_2.png) [@tedder](https://community.particle.io/u/tedder)\
**Post date:** [April 12, 2016, 4:34am UTC](https://community.particle.io/t/basic-electron-serial-reading-fails-works-on-photon/22021/3 "2016-04-12T04:34:27Z")

</div>

Okay. Thanks [mostly to this thread](https://community.particle.io/t/default-example-for-asset-tracker-gps-prints-erratic-nmea-sentences-to-serial/21356/38) I found out that I should use an inner loop to fetch the serial, rather than fetching one character on each loop().

Here’s the code I ended up using:

```
void loop() {
    if (Serial1.available() > 0 && Serial1.peek() != '$') {
        while (Serial1.peek() != '$' && Serial1.peek() != -1)
            Serial1.read(); // empty the buffer up to a new $ or end of buffer
    } else if (Serial1.available() > 0 && Serial1.peek() == '$') {
        while (Serial1.peek() != '\r' && Serial1.peek() != '\r') {
            char c = Serial1.read();
            if (gps.encode(c)) {
                onValidGpsSentence();
            }
        }
    }   
}

```

The documentation says both the Electron and Photon have the same serial buffer size (64 bytes), I assume that perhaps there’s more housekeeping work on the Electron?

---

<div class="post-metadata">

**Author:** ![ScruffR](https://sea2.discourse-cdn.com/flex026/user_avatar/community.particle.io/scruffr/32/6952_2.png) [@ScruffR](https://community.particle.io/u/ScruffR)\
**Post date:** [April 12, 2016, 3:43pm UTC](https://community.particle.io/t/basic-electron-serial-reading-fails-works-on-photon/22021/4 "2016-04-12T15:43:49Z")

</div>

This is advisable under any circumstance and on any platform to read all the data present.

So this should be part of most code that’s dealing with serial communication

```cpp
  ...
  while (Serial1.available())
  {
    int x = Serial1.read();
    doStuffWith(x);
  }
  ...

```

Once you are going up with baud and data rate on the Photon you’ll see the limited buffer there too.

---

<div class="post-metadata">

**Author:** ![tedder](https://sea2.discourse-cdn.com/flex026/user_avatar/community.particle.io/tedder/32/9646_2.png) [@tedder](https://community.particle.io/u/tedder)\
**Post date:** [April 12, 2016, 4:09pm UTC](https://community.particle.io/t/basic-electron-serial-reading-fails-works-on-photon/22021/5 "2016-04-12T16:09:27Z")

</div>

Yeah, ScruffR, sort of a “TIL”, I guess. As I said I assume the housekeeping on the Electron is longer, so I can’t rely on the buffer. It’s just a different mental model. Reading a sentence at a time seems to be really successful.