Carob Trees grow all over North America. I was able to forage a shopping bag full for free from the streets in Los Angeles and process about 3 pounds of powder in one weekend. The stuff is fairly easy to process at home, with the proper equipment. It helps to have a dehydrator and a VitaMix or some other kind of high powered blender, but a regular blender and a low temp oven might just do as well.
Step 1: Wash and boil
Clean your pods. They have probably been out in the world collecting all kinds of lovely smog and dust. I scrubbed 'em with some veggie wash. Carob is subject to mold and critters, but the ones I collected seemed pretty clean. I only picked the pods still on the trees, and only if they looked healthy and shiny.
The pods are kind of hard, and you want to get the seeds out, so unless you are fanatical about keeping your carob raw, boil them for about 20 minutes.
Step 2: Split pods
Once boiled, The pods can be slit with a sharp knife, longways to shuck the seeds. You are going to be eating the pods, not the seeds. You can even munch on the pods in this state as a kind of snack.
Step 3: Deseed
The seeds are pretty uniform in size and really hard. One can further process these to make an emulsifier for smoothies and ice cream, or use them in bean bags.
Step 4: Dehydrate
Once you have all your pods clean and de seeded, grind 'em up. I used a Cuisinart for this step. The pods are full of sugar, and if they are still damp from boiling that sugar can carmelize from the heat of blending. Then you end up with little sticky balls of sawdust, but that is ok, dried out these too will blend into powder.
You can dry the ground pods in the oven at low temp or in a dehydrator overnight. The dryer the stuff, the smoother your powder. Don't rush this step, it is key!