diff --git a/pxtarget.json b/pxtarget.json
index dfc84806..f7d9bd73 100644
--- a/pxtarget.json
+++ b/pxtarget.json
@@ -87,6 +87,95 @@
             "bluetooth": true,
             "thermometer": true,
             "compass": true
+        },
+        "boardDefinition": {
+            "visual": "microbit",
+            "gpioPinBlocks": [
+                [
+                    "P0"
+                ],
+                [
+                    "P1"
+                ],
+                [
+                    "P2"
+                ],
+                [
+                    "P3"
+                ],
+                [
+                    "P4",
+                    "P5",
+                    "P6",
+                    "P7"
+                ],
+                [
+                    "P8",
+                    "P9",
+                    "P10",
+                    "P11",
+                    "P12"
+                ],
+                [
+                    "P16"
+                ]
+            ],
+            "gpioPinMap": {
+                "P0": "P0",
+                "P1": "P1",
+                "P2": "P2",
+                "P3": "P3",
+                "P4": "P4",
+                "P5": "P5",
+                "P6": "P6",
+                "P7": "P7",
+                "P8": "P8",
+                "P9": "P9",
+                "P10": "P10",
+                "P11": "P11",
+                "P12": "P12",
+                "P13": "P13",
+                "P14": "P14",
+                "P15": "P15",
+                "P16": "P16",
+                "P19": "P19",
+                "P20": "P20"
+            },
+            "spiPins": {
+                "MOSI": "P15",
+                "MISO": "P14",
+                "SCK": "P13"
+            },
+            "i2cPins": {
+                "SDA": "P20",
+                "SCL": "P19"
+            },
+            "analogInPins": [
+                "P0",
+                "P1",
+                "P2",
+                "P3",
+                "P10"
+            ],
+            "groundPins": [
+                "GND"
+            ],
+            "threeVoltPins": [
+                "+3v3"
+            ],
+            "attachPowerOnRight": true,
+            "onboardComponents": [
+                "buttonpair",
+                "ledmatrix",
+                "speaker"
+            ],
+            "useCrocClips": true,
+            "marginWhenBreadboarding": [
+                0,
+                0,
+                80,
+                0
+            ]
         }
     },
     "compileService": {
diff --git a/sim/dalboard.ts b/sim/dalboard.ts
index 6049ebf8..1899b481 100644
--- a/sim/dalboard.ts
+++ b/sim/dalboard.ts
@@ -92,10 +92,9 @@ namespace pxsim {
 
             const options = (msg.options || {}) as RuntimeOptions;
 
-            const boardDef = CURRENT_BOARD; //TODO: read from pxt.json/pxttarget.json
-
+            const boardDef = msg.boardDefinition;
             const cmpsList = msg.parts;
-            const cmpDefs = msg.partDefinitions || {}; //TODO: read from pxt.json/pxttarget.json
+            const cmpDefs = msg.partDefinitions || {};
             const fnArgs = msg.fnArgs;
 
             const opts : visuals.BoardHostOpts = {
diff --git a/sim/definitions.ts b/sim/definitions.ts
deleted file mode 100644
index b48976e3..00000000
--- a/sim/definitions.ts
+++ /dev/null
@@ -1,59 +0,0 @@
-/// <reference path="../node_modules/pxt-core/typings/bluebird/bluebird.d.ts"/>
-/// <reference path="../node_modules/pxt-core/built/pxtparts.d.ts"/>
-/// <reference path="../node_modules/pxt-core/built/pxtsim.d.ts"/>
-/// <reference path="../libs/microbit/dal.d.ts"/>
-/// <reference path="./visuals/neopixel.ts"/>
-
-namespace pxsim {
-    export const MICROBIT_DEF: BoardDefinition = {
-        visual: "microbit",
-        gpioPinBlocks: [
-            ["P0"], ["P1"], ["P2"],
-            ["P3"],
-            ["P4", "P5", "P6", "P7"],
-            ["P8", "P9", "P10", "P11", "P12"],
-            ["P16"],
-        ],
-        gpioPinMap: {
-            "P0": "P0",
-            "P1": "P1",
-            "P2": "P2",
-            "P3": "P3",
-            "P4": "P4",
-            "P5": "P5",
-            "P6": "P6",
-            "P7": "P7",
-            "P8": "P8",
-            "P9": "P9",
-            "P10": "P10",
-            "P11": "P11",
-            "P12": "P12",
-            "P13": "P13",
-            "P14": "P14",
-            "P15": "P15",
-            "P16": "P16",
-            "P19": "P19",
-            "P20": "P20",
-        },
-        spiPins: {
-            MOSI: "P15",
-            MISO: "P14",
-            SCK: "P13",
-        },
-        i2cPins: {
-            SDA: "P20",
-            SCL: "P19",
-        },
-        analogInPins: ["P0", "P1", "P2", "P3", "P10"],
-        groundPins: ["GND"],
-        threeVoltPins: ["+3v3"],
-        attachPowerOnRight: true,
-        onboardComponents: ["buttonpair", "ledmatrix", "speaker"],
-        useCrocClips: true,
-        marginWhenBreadboarding: [0, 0, 80, 0],
-    }
-
-
-    //TODO: add multiple board support
-    export const CURRENT_BOARD = MICROBIT_DEF;
-}
\ No newline at end of file
diff --git a/sim/instructions.ts b/sim/instructions.ts
index 9a226073..71f7eec3 100644
--- a/sim/instructions.ts
+++ b/sim/instructions.ts
@@ -615,6 +615,9 @@ ${tsPackage}
                 });
         }
 
+        // board def
+        const boardDef = JSON.parse(getQsVal("board")) as pxsim.BoardDefinition;
+
         //parts list
         let parts = (getQsVal("parts") || "").split(" ");
         parts.sort();
@@ -638,7 +641,6 @@ ${tsPackage}
 
         style.textContent += STYLE;
 
-        const boardDef = CURRENT_BOARD;
         const cmpDefs = partDefinitions;
 
         //props
diff --git a/sim/microbit.ts b/sim/visuals/microbit.ts
similarity index 100%
rename from sim/microbit.ts
rename to sim/visuals/microbit.ts