magnet

Description: After reading Robert's article, there was a desire to build the project, leading to the ordering of an HMC 1001 sensor and the initiation of breadboarding the circuit. Several errors were identified in the schematic published in Sport Rocketry. The design was re-evaluated, resulting in a simplified circuit that functions effectively. Instead of amplifying and comparing outputs, a single op-amp was utilized as a comparator directly with the magnetic sensor. This configuration drives a Field Effect Transistor to activate a flashbulb or e-match circuit. It was determined that a voltage regulator was unnecessary, as the components are rated for up to 12 volts, allowing the use of a 9-volt battery without requiring the 5-volt supply from the regulator. Caution is advised, as the HMC 1001 can be damaged by voltages exceeding 12 volts. Honeywell recommends better circuit performance with a 5-volt supply, thus the regulator remains in the schematic. An alternative power supply option is the 544 battery, a compact 6-volt battery found in the photo section, slightly smaller than an "N" cell. Testing with a single Energizer 544 battery showed it could effectively fire smaller flashbulbs, although it lacked the power for larger AG-1 flashbulbs. Replacing the battery with a standard 9-volt allowed for successful firing of the AG-1 bulbs. For weight-sensitive applications, using two 544 batteries in series offers a near-perfect match to a single AA battery in terms of voltage. This configuration fits well within a 13mm body tube, which matches the outside diameter of an AA battery. A segment of 13mm body tube measuring 1 7/8" long can house two 544 batteries, allowing for a 12-volt power supply weighing about 1 ounce, compared to over 1 1/2 ounces for a single 9-volt battery. However, using this power supply necessitates the inclusion of the voltage regulator circuit to prevent damage to the HMC chip. Bench testing revealed a brief voltage surge through the flashbulb upon powering up or disconnecting the circuit. This phenomenon was observed with an LED during testing, indicating a potential leakage while the capacitor charges or a quirk in the op-amp or FET. To mitigate this risk, a shunt was added to the flashbulb, which is advisable regardless of the circuit design. This shunt may be a wire cut before launch or a jack with a shorted "remove before flight" plug. A power switch was incorporated at the positive battery terminal, although battery installation or removal could serve as an alternative power method if accessibility permits. The push-button switch in the circuit functions as the set/reset mechanism for the magnetic sensor, which may change orientation in the presence of a strong magnetic field.

The circuit design incorporates a HMC 1001 magnetic sensor, which is essential for detecting magnetic fields. The op-amp comparator is configured to provide a clear output signal based on the sensor's readings. The output from the op-amp is connected to a Field Effect Transistor (FET), which acts as a switch to control the flashbulb or e-match circuit. This arrangement allows for reliable ignition based on the magnetic field detected by the HMC 1001.

The choice of power supply is critical for the circuit's functionality and reliability. The 544 battery configuration, with two batteries in series, not only minimizes weight but also maintains the necessary voltage for effective operation. The circuit's design ensures that the HMC 1001 operates within its specified voltage range to prevent damage, while the inclusion of a voltage regulator adds an extra layer of protection.

The shunt added to the flashbulb circuit is a vital safety feature, preventing unintended ignition during power fluctuations. This precaution is important in any circuit design involving ignition systems. The use of a jack and plug for the shunt allows for easy disconnection before launch, enhancing safety.

Overall, this circuit provides a robust solution for applications requiring magnetic field detection and ignition systems, with considerations for weight, power supply, and safety features integrated into the design.After reading Robert`s article, I immediately wanted to build this project so I ordered an HMC 1001 sensor and started breadboarding the circuit. As it turns out, there were a couple errors in the schematic that appeared in Sport Rocketry. I took Robert`s design apart and did a bit of redesigning to make it work. There has since been a correction published, but I had already come up with a much simpler circuit that works perfectly. Instead of trying to amplify then compare the outputs, I simply used a single op-amp as a comparator right off the magnetic sensor. Like the original, this drives a Field Effect Transisor to fire a flashbulb (or e-match) circuit. I also found that the voltage regulator really isn`t neccessary. The components are rated for up to 12 volts, so a 9 volt battery could be used to power everything without having the 5 volt power supply from the regulator.

Be cautious as the HMC 1001 can be damaged if it sees more than 12 volts. According to Honeywell, the circuit performs better with a 5 volt supply, so I have left the regulator in this schematic. Another option on the power supply is to use the 544 battery. This is a small 6 volt battery found in the photo section. The battery is a little smaller than an "N" cell and measures about 1/2" diameter and 1" long. They are also available in Lithium. I built a circuit without a voltage regulator using a single Energizer 544 battery. It was able to fire the smaller flashbulbs taken from flash cubes very well, but didn`t have the power to handle the larger AG-1 flashbulbs.

Of course it was easy to simply replace that battery with a standard 9 volt and it will fire the AG-1 bulbs just fine. I haven`t done any testing with electric matches or any other type of ignitor. For the serious weight conscious project and to guarantee that you have the power to fire your ejection charges, an idea I came up with here is to use two 544s in series.

Two of these little batteries end to end are just about a perfect match to a single AA battery. The diameter is slightly less, but guess what They fit perfectly inside a piece of 13mm body tube, which just happens to have the same outside diameter as an AA battery. So cut a 1 7/8" long piece of 13mm body tube, slide in two 544 batteries, and put it in a standard AA battery holder.

You now have a 12 volt power supply that weighs about 1 ounce compared to over 1 1/2 ounces just for a single 9 volt battery. Not to mention the reduced size. Pretty sweet, eh If you use this power supply, you have to use the voltage regulator circuit or you risk damage to the HMC chip.

Another noteworthy item that came up during bench testing was that when you first power up or even disconnect the circuit, there is a very brief surge of voltage that will go through the flashbulb. I was using an LED on the bench during my testing in place of the flashbulb, and it flashed every time you turn the power on or off.

This is apparently a leak through while the capacitor is charging, or may be a quirk in either the op amp or the FET. Either way, it could cause the flashbulb to fire, so I added a shunt to the flashbulb (which you ought to do anyway, no matter what circuit you are using).

This could either be a piece of wire that you cut just before leaving the rocket on the pad, or a jack with a shorted "remove before flight" plug. I set mine up with a jack and plug setup. Just make sure the plug is in place before connecting the flashbulb and before turning on or off the power.

Although I put a power switch on mine (SPST slide switch at the positive battery terminal), you could just install or remove the battery to power it up if the battery will be readily accessable. The push button switch in this circuit is the set/reset circuit for the magnetic sensor. If it is exposed to a strong magnetic field, the orientation of the sensor can be changed. The HMC circuit has a built in coil to apply a small cor