Hi
I'm working on a device that will detect the vibration of a projectile's impact on a giant latex balloon and then allow sufficient current to pass through a heating element to explode the balloon.
In truth, I have managed to create a working prototype, firstly using an Arduino UNO, and then an Arduino NANO (in an attempt to reduce the physical size). In both cases, the circuit was powered by 9 volts from 6xAA batteries. A piezo disc detected the vibration of impact, the Arduino switched an output pin HIGH connected to the base of the TIP122 which allowed current from the 6xAA to flow through an Estes Solar Rocket Starter as the heating element. Worked well. You can see the result in action here.
In order to shrink/improve the device, even more, I am trying to replace the Arduino NANO with an ATTiny85V and the Rocket Starter with a Remote Control Engine Glow Plug but I am having trouble and hope for some advice.
The ATTiny85V is being powered by 2xAA batteries.
The Glow Plug can use a 1.5 - 3.0V power supply and draws around 2.5 amps from that supply for the 1.5 seconds that it is switched on.
I have attached a schematic of my test circuit. It doesn't include the piezo sensor because that 'side' of the circuit works as planned. It only includes the 'ignition' side of the circuit which I can't get working.
PB3 on the ATTiny85V switches HIGH when the push button switch is activated. In turn, PB2 is then switched HIGH supplying current to the base of the TIP122 transistor, allowing the flow of current through the Glow Plug Igniter for 1.5 seconds.
The 3V supply on the schematic is provided by a pair of AA batteries.
Problem is, I can't get sufficient current to flow through the Glow Plug and I don't understand why.
I have used various size resistors at R2 without success. I have even removed R2 all together (bad option, I have learned) but still the Glow Plug would not glow.
Am I asking too much of the TIP122? Is there a better option?
The Glow Plug glows immediately if connected directly to even a single 1.5V AA battery, but not if connected via the transistor.
Hopefully
LB
Moderator edit: PDF. Ugh.
attiny85v-pushbutton-test.pdf (403 KB)