Tiny BASIC guide

OrbitDeck for iOS includes a self-contained Tiny BASIC interpreter (Operating Tools → Tiny BASIC). It is source-compatible with the BASIC on the OrbitDeck desktop app and CardSat, and adds live satellite, station, pass, space-weather and geomagnetic data as read-only variables, a 240 × 135 graphics display, and a sandboxed file store. This guide documents the full dialect as implemented in the app.

The workspace

The Tiny BASIC screen has two panes — a program editor and a graphics display — side by side on a wide iPad and stacked on iPhone.

Program — a monospaced editor. Type or paste your program here.
Run — executes the program from the top. Text output appears in the Output box and drawing appears on the Display.
Clear — empties the Output box and the Display (it does not change your program).
Actions menu — Open file… loads a .txt program from the Files app, Load sample restores the built-in demo, and Share source exports your program text via the iOS share sheet.
Output — everything PRINT produces, selectable for copying. A status line below reports how many statements ran and how many graphics calls were made, or the error if one occurred.
Display · 240 × 135 — the graphics surface (see Graphics).
INPUT values — if your program uses INPUT, a panel appears listing each prompt so you can fill in the values before you press Run (see INPUT).

Errors are reported in the Output box beginning with ?, mirroring classic BASIC — for example ?divide by zero. The status line repeats the message.

Program structure

A program is a list of numbered lines, lowest number first:

10 PRINT "HELLO, ORBIT"
20 FOR I=1 TO 3
30 PRINT I
40 NEXT
50 END

Line numbers order the program and are the targets of GOTO, GOSUB, IF…THEN n and ON…GOTO.
Several statements per line may be separated by a colon : — for example 10 A=1: B=2: PRINT A+B.
Keywords are case-insensitive (print = PRINT). Variable and function names are treated as upper-case.
Comments use REM; everything to the end of the line is ignored. DATA lines are likewise skipped during normal execution and read only by READ.
Immediate mode — a program with no line numbers runs its statements top to bottom, but flow-control statements that need line targets (GOTO, GOSUB, RETURN, DATA, READ, RESTORE) require a numbered program and will report an error in immediate mode.

Because the colon splits a line into independent statements, only the statement immediately after THEN is guarded by an IF. In 10 IF X>0 THEN PRINT "POS" : PRINT "ALWAYS", the second PRINT runs regardless of X. Put conditional work on its own line or branch with THEN lineNumber.

Variables & arrays

Numeric variables

Numeric variables are a single letter A–Z and hold double-precision floating-point values. Assignment may use LET or omit it:

10 LET A=3.5
20 B=A*2
30 PRINT B

String variables

String variables are a single letter followed by $ — A$–Z$. Join strings with +:

10 N$="OSCAR"
20 PRINT N$ + "-100"

Arrays

Arrays are declared with DIM and are zero-based — DIM A(12) creates indices 0…11. Two kinds exist:

Named arrays share the letter namespace with functions but are separate from the same-letter scalar: DIM A(10) then A(3)=7. A scalar A and the array A(…) are independent.
The anonymous array @() — a single unnamed array: DIM @(6) then @(0)=2.
Clear a named array with ERASE name.

A named array may hold up to 1024 elements and the anonymous array up to 256, with a combined budget of 2048 elements across all arrays.

10 DIM A(12),@(6)
20 DATA 2,3,5,7,11,13
30 FOR I=0 TO 5: READ @(I): NEXT
40 A(0)=100
50 PRINT @(2), A(0)

Operators & expressions

Numeric operators, from lowest to highest precedence:

Level	Operators	Notes
Logical OR	`OR`	Result is 1 (true) or 0 (false)
Logical AND	`AND`	1 or 0
Comparison	`=` `<>` `<` `>` `<=` `>=`	Return 1 or 0
Add / subtract	`+` `-`
Multiply / divide / modulo	`*` `/` `%` `MOD`	`%` and `MOD` are the same truncating remainder
Power	`^`	Right-associative
Unary	`-` `+` `NOT`	`NOT` yields 1 for a zero operand, else 0

Comparison and logical operators produce 1 for true and 0 for false, so they can be used directly in arithmetic. Parentheses group as usual. Dividing or taking a remainder by zero raises ?divide by zero.

Strings concatenate with + and compare with the same relational operators (=, <>, ordering by Unicode). A relation is treated as a string comparison when either side looks like a string (a literal in quotes or a $ variable/function).

Trigonometric functions work in degrees, not radians — SIN(30) is 0.5. Use the RAD and DEG constants to convert if you need radians.

Statements

Statement	Purpose
`LET v=expr`	Assign a value. `LET` is optional. Targets: scalars, `A$`–`Z$`, `A(i)`, `@(i)`.
`PRINT items` · `?`	Print text and numbers. `?` is shorthand. See below for separators.
`LPRINT items`	Like `PRINT` but the line is prefixed with `[LPRINT]` (a stand-in for a printer).
`INPUT v[,v…]`	Read values supplied in the INPUT panel before the run. Numeric or `$` variables.
`IF cond THEN …`	If the condition is non-zero, run the statement after `THEN`; if `THEN` is followed by a bare line number, jump there.
`FOR v=a TO b [STEP s]` … `NEXT`	Counted loop; default step 1. Negative steps count down.
`GOTO n`	Jump to line n.
`GOSUB n` … `RETURN`	Call a subroutine and return to the following statement.
`ON expr GOTO n1,n2,…`	Jump to the expr-th line number (1-based); out-of-range falls through.
`DIM name(n)` · `DIM @(n)`	Declare arrays. Multiple declarations may be comma-separated.
`ERASE name`	Discard a named array.
`DATA v1,v2,…`	Inline numeric constants read by `READ`.
`READ v[,v…]`	Read the next `DATA` value(s) into variables or array elements.
`RESTORE`	Rewind the `DATA` pointer to the beginning.
`REM text`	Comment to end of line.
`END` · `STOP`	End the program.
`CLS PSET LINE CIRCLE TEXT SHOW`	Graphics — see Graphics.
`FOPEN FPRINT FCLOSE FILES`	Sandboxed files — see Files.
`SATSEL i` · `TXSEL i`	Choose a satellite / transponder for the live variables — see below.

PRINT formatting

Separate PRINT items with commas or semicolons:

Comma inserts two spaces between items (a light column effect).
Semicolon joins items with no space.
A trailing comma or semicolon suppresses the line break, so the next PRINT continues the same line. A PRINT with no arguments flushes the pending line.
Whole numbers print without a decimal point; other values use a compact general format.

10 A=42: N$="ISS"
20 PRINT "SAT ", N$, "CODE"; A

produces SAT ISS CODE42.

INPUT

OrbitDeck collects INPUT values before the program runs rather than pausing mid-run. When your program contains INPUT statements, an INPUT values panel lists each prompt (its label text and the target variable); fill them in, then press Run. Values are consumed in order. A missing numeric value is 0; a missing string is empty.

10 INPUT "YOUR ALTITUDE KM"; A
20 INPUT "CALLSIGN"; C$
30 PRINT C$ + " AT " ; A ; " KM"

Functions

Numeric functions

Function	Returns
`ABS(x)`	Absolute value
`INT(x)`	Floor (largest integer ≤ x)
`ROUND(x)`	Nearest integer
`FRAC(x)`	Fractional part
`SGN(x)`	−1, 0, or 1
`SQR(x)`	Square root (of max(0, x))
`EXP(x)`, `LOG(x)`, `LOG10(x)`	Exponential and natural / base-10 logs
`SIN(x)`, `COS(x)`, `TAN(x)`	Trig, argument in degrees
`ASN(x)`, `ACS(x)`, `ATN(x)`	Inverse trig, result in degrees
`ATN2(y,x)`	Two-argument arctangent, degrees 0…360 range via atan2
`MIN(a,b)`, `MAX(a,b)`, `HYP(a,b)`	Minimum, maximum, hypotenuse
`RND` · `RND(n)`	Random 0…1; with an argument, a random integer 0…n−1

String functions

Function	Returns
`LEFT$(s,n)`, `RIGHT$(s,n)`	First / last n characters
`MID$(s,start[,len])`	Substring from 1-based `start`, optional length
`CHR$(n)`	Character for byte value n
`STR$(x)`	Number formatted as text
`UCASE$(s)`, `LCASE$(s)`, `TRIM$(s)`	Upper / lower case, trim whitespace
`GRID$(lat,lon)`	Four-character Maidenhead locator
`DXCC$(code)`	Name of the DXCC entity for an ARRL numeric code
`TIME$`, `DATE$`	Current UTC `HH:MM:SS` and `YYYY-MM-DD`

String-to-number functions

Function	Returns
`LEN(s)`	Character count
`ASC(s)`	Byte value of the first character
`VAL(s)`	Number parsed from text (0 if none)
`INSTR(hay,needle)`	1-based position of `needle` in `hay`, or 0

Geo & RF helpers

Function	Returns
`GCDIST(lat1,lon1,lat2,lon2)`	Great-circle distance in km
`GCAZ(lat1,lon1,lat2,lon2)`	Initial great-circle bearing in degrees
`FSPL(freqMHz,distKm)`	Free-space path loss in dB
`DXCCLAT(code)`, `DXCCLON(code)`	Reference latitude / longitude for a DXCC entity
`PASSAOS(k)`, `PASSLOS(k)`, `PASSMAX(k)`	For the k-th upcoming pass of the selected satellite: minutes to AOS, minutes to LOS, and maximum elevation (degrees). Index 1…`PASSN`.

Constants

Name	Value
`PI`	π
`TWOPI`	2π
`DEG`	Degrees per radian (180/π)
`RAD`	Radians per degree (π/180)
`CLIGHT`	Speed of light, 299 792 458 m/s
`KBOLT`	Boltzmann constant, 1.380649×10⁻²³
`REARTH`	Earth radius, 6378.137 km

Live data variables

The interpreter exposes OrbitDeck's live state as read-only numeric variables. They are populated from your station, the selected satellite, the current pass prediction, the Sun and Moon, space weather, and a planning-grade geomagnetic model at run time. Many "OK" flags are 1 when the corresponding data is available and 0 otherwise, so you can guard on them.

Time (UTC)

Variable	Meaning
`UTCH UTCM UTCS`	Hour, minute, second
`UTCDAY UTCMON UTCYR`	Day, month, year
`LSTHR`	Local sidereal time, hours
`TIMEOK`	1 when the clock is set (also gates `TIME$`/`DATE$`)

Station

Variable	Meaning
`MYLAT MYLON MYALT`	Observer latitude, longitude, altitude (m)
`MAGDECL`	Approximate magnetic declination (degrees, east positive)
`NSAT NFAV`	Catalog size and number of favorites
`POSOK`	1 when the station position is known

Selected satellite

Variable	Meaning
`SATAZ SATEL`	Azimuth and elevation (degrees)
`SATRNG SATRR`	Slant range (km) and range rate (km/s)
`SATLAT SATLON SATALT`	Sub-point latitude, longitude, altitude (km)
`SATSUN`	1 if the satellite is sunlit
`SATINC SATECC SATRAAN SATMM`	Inclination, eccentricity, RAAN, mean motion
`SATNOR`	NORAD catalog number
`GPAGE`	Element-set age in days
`DECAYD DECAYSRC`	Estimated decay lifetime (days) and its source (1 n-dot, 2 B*)
`SATOK`	1 when satellite look angles are valid

Next pass

Variable	Meaning
`AOSIN LOSIN`	Minutes to AOS / LOS of the next pass
`PASSEL`	Maximum elevation of the next pass (degrees)
`PASSVIS`	1 if the next pass is optically visible (satellite sunlit, Sun below −6°)
`PASSN`	Number of upcoming passes found (up to 8)
`PASSOK`	1 when a pass was found

Use PASSAOS(k), PASSLOS(k) and PASSMAX(k) to read individual passes 1…PASSN.

Sun & Moon

Variable	Meaning
`SUNAZ SUNEL`	Sun azimuth and elevation (degrees)
`MOONAZ MOONEL`	Moon azimuth and elevation (degrees)

Space weather

Variable	Meaning
`SFI`	10.7 cm solar flux
`SSN`	Sunspot number
`KP AINDEX`	Planetary Kp and A index
`MUF`	Modeled daytime MUF
`SPWXOK`	1 when space-weather values are available

Transponder (after `TXSEL`)

Variable	Meaning
`NTX`	Number of transponders on the satellite
`TXDL TXUL TXBW`	Downlink center, uplink center, bandwidth (Hz)
`TXINV TXLIN`	1 if inverting / linear
`DOPPRX DOPPTX`	Doppler-corrected downlink / uplink dial frequencies (Hz)
`TXOK`	1 when a transponder is selected

Geomagnetic (planning-grade dipole)

Variable	Meaning
`LSHELL`	McIlwain L-shell at the sub-point
`BFIELD BRATIO`	Field magnitude (nT) and B/B₀ ratio
`INBELT INSAA`	1 inside a radiation belt / South Atlantic Anomaly

Several host variables are defined for source-compatibility with CardSat firmware (for example GPS, battery, heap and additional space-weather fields such as FLARE, BZ, SWSPEED). On iOS these read 0 unless OrbitDeck has a value for them; guard on the matching "OK" flag where one exists. The geomagnetic figures use the same centered-dipole model as Orbital Zones, not a full IGRF model.

Selecting satellites & transponders

By default the live variables describe OrbitDeck's currently selected satellite. Inside a program you can switch context:

SATSEL i — select catalog index i (0-based) and refresh all SAT…, pass and geomagnetic variables, plus the PASSAOS/PASSLOS/PASSMAX tables. It clears any transponder selection.
TXSEL i — select transponder index i (0-based) on the current satellite and populate TX… and DOPPRX/DOPPTX.

10 REM Report the next pass of catalog entry 0
20 SATSEL 0
30 IF PASSOK=0 THEN 60
40 PRINT "SAT ", SATNOR, " NEXT AOS ", ROUND(AOSIN), " MIN, MAX EL ", ROUND(PASSEL)
50 END
60 PRINT "NO PASS FOUND"

Graphics & display

The display is 240 × 135 pixels; (0,0) is the top-left corner. Colors are an index 0…9 into the palette:

Index	Color	Index	Color
0	Black	5	Yellow
1	White	6	Teal
2	Red	7	Orange
3	Green	8	Gray
4	Blue	9	Dark green

Statement	Effect
`CLS`	Clear the display to black
`PSET x,y[,c]`	Plot a point (color defaults to 1)
`LINE x1,y1,x2,y2[,c]`	Draw a line
`CIRCLE x,y,r[,c]`	Draw a circle outline
`TEXT x,y,value`	Draw text (a string or a number) at x,y
`SHOW`	Marker to present the frame (drawing is shown after the run regardless)

Files & storage

Programs can write small text files, confined to OrbitDeck's private Application Support/OrbitDeck/Basic directory. Programs cannot supply paths or escape that sandbox.

Statement	Effect
`FOPEN "name"`	Open (creating if needed) a file for appending
`FPRINT items`	Append a line to the open file (same item rules as `PRINT`)
`FCLOSE`	Close the open file
`FILES`	Print the list of files in the sandbox

File names may be up to 40 characters of letters, digits and _ . -; they may not start with a dot or contain a slash.

Limits & safety

Execution is bounded so a runaway program cannot hang the app:

Limit	Value
Statements per run	2,000,000 (then too many statements)
Wall-clock time	~10 seconds (then program ran too long)
Nested `FOR` loops	8
`GOSUB` depth	16
Total array elements	2048 (named ≤ 1024, anonymous ≤ 256)

Division or modulo by zero, out-of-range array indices, RETURN without GOSUB, NEXT without FOR, and unknown names all raise a descriptive ? error.

Worked examples

The built-in sample

The Load sample action loads this program, which exercises arrays, DATA/READ, graphics and live variables:

10 REM OrbitDeck Tiny BASIC
20 DIM A(12),@(6)
30 DATA 2,3,5,7,11,13
40 FOR I=0 TO 5: READ @(I): NEXT
50 CLS
60 FOR I=0 TO 11
70 A(I)=50+20*SIN(I*30)
80 LINE 120,67,120+95*COS(I*30),67+A(I)*SIN(I*30),3
90 NEXT
100 CIRCLE 120,67,30,5
110 TEXT 70,4,"ORBITDECK BASIC"
120 PRINT "MY GRID DATA: LAT=",MYLAT," LON=",MYLON
130 IF SATOK=0 THEN 160
140 PRINT "SAT ",SATNOR," AZ=",ROUND(SATAZ)," EL=",ROUND(SATEL)
150 PRINT "NEXT AOS IN ",ROUND(AOSIN)," MIN"
160 SHOW
170 END

A pass table for the selected satellite

10 IF PASSOK=0 THEN 70
20 PRINT "PASS  AOS(MIN)  LOS(MIN)  MAXEL"
30 FOR K=1 TO PASSN
40 PRINT K, ROUND(PASSAOS(K)), ROUND(PASSLOS(K)), ROUND(PASSMAX(K))
50 NEXT
60 END
70 PRINT "NO PASSES IN THE WINDOW"

Great-circle distance to a DXCC entity

10 REM 291 = United States reference point
20 D=GCDIST(MYLAT,MYLON,DXCCLAT(291),DXCCLON(291))
30 B=GCAZ(MYLAT,MYLON,DXCCLAT(291),DXCCLON(291))
40 PRINT DXCC$(291)
50 PRINT "RANGE ", ROUND(D), " KM  BEARING ", ROUND(B), " DEG"

Logging to a file

10 FOPEN "log.txt"
20 FPRINT DATE$, " ", TIME$, " SFI=", SFI, " KP=", KP
30 FCLOSE
40 FILES

Compatibility notes

This interpreter is designed to run the same programs as the OrbitDeck desktop app and CardSat. A few platform notes:

INPUT is collected up front through the INPUT panel rather than pausing execution.
PASSAOS/PASSLOS/PASSMAX accept indices 1…PASSN; index 0 is accepted as an alias for the first pass for compatibility with early program versions.
Host variables that OrbitDeck cannot supply on iOS (some CardSat hardware telemetry) read 0; check the relevant "OK" flag.
The geomagnetic variables use OrbitDeck's centered-dipole planning model, not CardSat's IGRF precision.

Share your programs with Actions → Share source, and reopen saved .txt programs with Actions → Open file….