How to add shadows to surface shader?

This is a question I've seen around a lot but the shader I'm using seems to resist any solutions I've tried. It's a sort of echolocation shader that behaves like this, made by jinglebiscuits that I modified and would like to add shadows to.

Here's my shader code. Please note I'm a total beginner when it comes to shaders so I don't understand much yet:

 Shader "My/Normal/AlphaPulseShader" {
     Properties {
       _MainTex ("Base (RGB) Trans (A)", 2D) = "blue" {}
       _BumpMap ("Normalmap", 2D) = "bump" {}
       _EmissionMap ("Emission Map", 2D) = "black" {}
       _Color ("Color", Color) = (1, 0, 0, 1)
       _PDistance("PulseDistance", Float) = 0
       _PFadeDistance("FadeDistance", Float) = 10
       _PEdgeSoftness("EdgeSoftness", Float) = 5
       _Origin("PulseOrigin", Vector) = (0, 0, 0, 0)
       
       _RimColor("Rim Color", Color) = (1,1,1,1)
       _RimPower("Rim Power", Range(0.5, 8.0)) = 1.059702
       _RimOn("Rim On", Range(0, 1)) = 0.0
       _EmissionMultiplier("Emission Multiplier",Range(-10,10)) = 1.0
     }
     
     SubShader {
       Tags {"Queue"="Transparent" "IgnoreProjector"="True" "RenderType"="Transparent"}
       LOD 200
 
       ZWrite On
       ZTest LEqual
       Blend SrcAlpha OneMinusSrcAlpha
 
       CGPROGRAM
 
       //LIGHTING
       #include "AutoLight.cginc"
 
       // define finalcolor and vertex programs:
       #pragma surface surf Lambert finalcolor:mycolor vertex:myvert// alpha
       struct Input {
           float2 uv_MainTex;
           float2 uv_BumpMap;
           float2 uv_EmissionMap;
           float3 worldPos;
           float3 viewDir;
           half alpha;
       };
       
       fixed4 _Color;
       sampler2D _MainTex;
       sampler2D _BumpMap;
       sampler2D _EmissionMap;
       half _PDistance;
       half _PFadeDistance;
       half _PEdgeSoftness;
       float4 _Origin;
       
       float4 _RimColor;
       float _RimPower;
       float _RimOn;
       float _EmissionMultiplier;
 
       void myvert (inout appdata_full v, out Input data) {
           UNITY_INITIALIZE_OUTPUT(Input, data);
  
 
       }
       
       void mycolor (Input IN, SurfaceOutput o, inout fixed4 color) {
           // set the vertex color alpha to the value calculated: 
           fixed4 c = tex2D(_MainTex, IN.uv_MainTex) * _Color;
           color.a = c.a;
           half dis;
           half interval;
           half origin;
           dis = sqrt(pow((IN.worldPos.x - _Origin.x),2) + pow((IN.worldPos.y - _Origin.y), 2) + pow((IN.worldPos.z - _Origin.z), 2));
           
           if(dis >= _PDistance)
           {
               color.rgb = color.rgb * (1 - saturate(abs(_PDistance - dis)/_PEdgeSoftness));
           }
           else
           {
               color.rgb = color.rgb * (1 - saturate(abs(_PDistance - dis)/_PFadeDistance));
           }
           
       }
       
       void surf (Input IN, inout SurfaceOutput o) {
           // simply copy the corresponding texture element color:
           fixed4 c = tex2D(_MainTex, IN.uv_MainTex) * _Color;
           o.Albedo = c.rgb;
          // o.Alpha = tex2D(_MainTex,IN.uv_MainTex).a;
           o.Normal = UnpackNormal(tex2D(_BumpMap, IN.uv_BumpMap));
         //  half rim = 1.0 - saturate(dot(normalize(IN.viewDir), o.Normal));
           if(_RimOn > 0)
          {
               half rim = 1.0 - saturate(dot(normalize(IN.viewDir), o.Normal));
               o.Emission = _RimColor.rgb * pow(rim, _RimPower) + _EmissionMultiplier*tex2D(_EmissionMap,IN.uv_EmissionMap);
           }
       }
       
       ENDCG
     } 
 
    // Fallback "Diffuse"
         Fallback "VertexLit"
 
   }

Anyone have any idea how I could do this?