MIT app inventor gas sensor alarm

[blacks pro]

I am new to the mit app inventor and i just build a gas sensor alarm that can control the value when the alarm will be triggered with a slider. I keep on facing the cannot accept the argument {empty string } as shown below. Can anoyone help me figure it out how to solve this problem. Thank you!!

[gerrikoio]

I keep on facing the cannot accept the argument {empty string }... 

As you may know, this is a runtime error message. So, usually to problem solve these sort of things, one needs to know when it happened. What did you do to trigger the error message? I'm guessing it happened after you picked something off a list.

[blacks pro]

The error is triggered when i connect my app to the bluetooth and starts to receive numbers.The error appears 5-10 seconds everytime after i dismiss it.

[Abraham Getzler]

Your test for input is incomplete.

It only has one level, connectivity.

It also has to test for data arrival.

The proper sequence in the Clock Timer is:

IF CONNECTED THEN

   IF BytesAvailable > 0 THEN

      set Label1.Text to (Get the text from BlueTooth)

ABG

P.S.  What are you doing to send the data? 

print or println?

That affects your delimiter usage.

FAQ: https://groups.google.com/forum/?utm_medium=email&utm_source=footer#!msg/mitappinventortest/2cd6Uz__xA0/cPQSiZpcDAAJ

[Abraham Getzler]

post your .ino file here,

so we can see the next error.

Also, Ask yourself what you will get into your Label

if you ask for bytes from BlueTooth regardless of whether

there are bytes available to be read, or not?

Search this forum for "gas sensor".

You are not the first.

ABG

[blacks pro]

I think i might want bytes available to read because its same with my serial monitor.

(.apk removed, per board restrictions - ABG)

[blacks pro]

Please dont mind if i put the label box with text box.

[Abraham Getzler]

(.apk removed per board guidelines)

I see you are using println() in your .ino sketch to send the reading.

That means that you are using the NL (New Line) character as a line delimiter,

and that to have your AI2  app receive exactly one line at a time,

and no blanks or partial messages, you need to follow the AI2 Delimiter

strategy at this Faq post:

https://groups.google.com/d/msg/mitappinventortest/lVaCyAeWm_4/ADjvy05wAwAJ

ABG

 const int gasPin = A0;  

 

int sensorValue = 0;        

int outputValue = 0;        

void setup() {

  Serial.begin(9600);

}

void loop() {

   int analogVal = analogRead(gasPin);

  Serial.println(analogVal);

  delay(1000);

  float IniVol = 75.0 / 1023.0 * 5.0;

  float FinalVol = analogVal / 1023.0 * 5.0;

  float ChangVol = FinalVol - IniVol;

  float ppm = 407.25 + 2800.0 * ChangVol;

 

[blacks pro]

I think i have solve the problem with changing the println to print and add a new block as shown below.

[Abraham Getzler]

I think i have solve the problem with changing the println to print

Things that might still go wrong ...

How do the transmission and reception rates compare?

What will happen if two transmissions happen in the time span 

of a single Clock1.Timer event?  Will the input be the concatenation of two

transmissions, so if the device send 7 and then 9 the app will receive 79?

ABG

[blacks pro]

There is sometime when the clock timer receive two transmission. Sometime the app will receive 179180 which is 179 and 180.

How to solve this problem?

[Abraham Getzler]

Sometime the app will receive 179180 which is 179 and 180

You just discovered the purpose of a Delimiter.

See this post from the FAQ:

https://groups.google.com/d/msg/mitappinventortest/lVaCyAeWm_4/ADjvy05wAwAJ

ABG

 P.S.  You will need to switch back to println() for this to work.

(edit)

[blacks pro]

How do I put Delimiter in my case?

[blacks pro]

I dont really know whats the meaning of delimiter and what is the function of it.

[Abraham Getzler]

See attached.

ABG

[Abraham Getzler]

2:59 PM (4 minutes ago)

I dont really know whats the meaning of delimiter and what is the function of it.

https://www.google.com/search?q=define+delimiter

For this app, the LF is the delimiter between transmissions.

ABG

 

[blacks pro]

What is LF?

[blacks pro]

Like this?

[Abraham Getzler]

See the attachment?

LF = Line Feed, also known as New Line

ABG

[blacks pro]

Then what block do i need to use to replace the call.Bluetooth client.bytes available to receive

[Abraham Getzler]

-1