WSN application – insulin dosage monitor
Insulin dependent diabetics often face this problem . Sometimes they forget to inject insulin and other times they inject insulin but cannot remember that they have done so. If a diabetic forgets to inject insulin then her blood sugar will shoot up (a medical condition called hyperglycemia) and if she injects too much insulin, her blood sugar can quickly drop ( hypoglycemia). Both conditions are dangerous.
Let us take the case in which a person is not sure that they have taken insulin. Given the fact that even fast acting insulin takes some time to act she would have to wait for a while and re-test her blood sugar level couple of times (using a glucometer) before she can be sure that she has taken an insulin shot or not. This can be a frustrating experience if you are busy at work or are about to go out somewhere.
In the other scenario, a diabetic can completely forget to take insulin.
A simple insulin dosage monitoring system can be built using a low tech reed switch and couple of wireless sensor nodes. It can help in both the scenarios mentioned above.
This idea will work with the “NovoPen 3” and other insulin pens which have similar delivery mechanism. According to Novo Nordisk, the “NovoPen 3 is one of the most widely used durable insulin pens in the world”. It seems to be the preferred delivery mechanism today in India.
The “NovoPen 3” s has three components. One is a disposable needle, the second is a replaceable insulin cartridge and the third is a dose dialing mechanism consisting of (among other things) a knob at the end of the pen. This knob has be turned/dialed according to the number of units needed and then pushed in to deliver the dialed dose. This knob is more like a screw head. When a screw is turned, the screw head moves in and out depending on the direction of rotation. This knob can only be turned in one direction such that it moves out of the pen. It can only be pushed in to deliver the dosage.
The idea involves –
- Sticking a tiny magnet to the knob at the end of the pen.
- Attaching a snap on wireless node to the Pen body. This node will have a reed switch as close as possible to the knob but not touching it. This wireless node should be removable. It has to be very low profile and should not impact the pen’s handling in any way.
How does it work ?
Knob in default position (reed switch is closed)
Knob in dialed position (reed switch is open)
When a dose is dialed, the knob and therfore the magnet moves out of the pen and away from the reed switch. When the knob is pushed in the magnet goes back to its original position (right next to the reed switch). Assuming we have a normally open reed switch, the switch will stay closed when the pen is not in use since the magnet will be positioned next to the switch. When a dose is dialed, the switch will open since the magnet will move away from the switch. The dose amount will determine how much distance the magnet will move away from the switch. The switch and magnet should be carefully positioned to ensure that the switch opens even when small doses are dialed. Now we have a way to detect insulin delivery.
- The switch is initially closed
- When a dose is dialed, the switch opens
- When the dialed dose is injected, the switch closes
The micro in the node can detect these switch open/close events using interrupts.
The wireless node can simply send an SMS whenever it detects insulin delivery. It can also send an SMS if it does not detect insulin delivery during the portions of the day when insulin is expected to be injected.
This sensor node can be enhanced to do other things such as monitoring ambient temperature and light. I have written another article describing the same in detail.