JCM inVentures Inc.
Here are the schematics for the Cybug Hornet BEAM robot...
Steering Control logic.
The optical sensors on the Hornet consist of two Green LED's placed on either side of the robot's head. Light shining onto LED's produce a small varying voltage proportional to the intensity of the light. The relative voltage of each led is compared by U1A, which, in turn, produced either a V+ voltage or a ground potential. ( V+ if the positive + input voltage is greater than the - input )
If U1A produces the V+ voltage level, the darlington transistor Q1 is turned on, enabling the RIGHT motor M1. U1B produces the opposite output condition to transistor Q2, which disables the motor M2.
If U1A produces a ground potential at it's output, Q2 is turned ON, enabling M2. This is how the Hornet is influenced to steer toward the light.
Backup control logic.
The two switches, S1 & S2, are the two feeler touch-sensors on the front of the Hornet. If, say, S1 were to be closed, the voltage off the light sensor, D1, would drop to zero and be held at a low condition as the capacitor C2 slowly charges up. While in that low condition, the control circuitry would naturally choose D2 as the "brighter" eye and cause the robots behaviour to favour that side.
The Dynamic Solar Engine ( DSE )
The dynamic solar engine has been designed by JCM InVentures to adjust it's voltage trigger thresholds to compensate for low light levels automatically.
This schematic is a simplified version of the schematic to demonstrate how the DSE works. There are actually more resistors in series and parallel configurations around the Max8212 (U2) to create the correct resistances for the Hornet.
Dynamic Solar Engine DSE ( cont'd)
The Max 8212 programmable voltage detector is a useful, adjustable device which uses external resistors to determine the maximum and minimum trigger points based on the formula's shown on page 5 of the chips specification sheet ( over here on the MAXIM site ). The value between these two trigger points is called hysterisis or "dead zone". We've created a spreadsheet for you to use to avoid using the formula's, and simply add in the resistances.
The top table will let you play with the upper and lower trigger points ( Vu & Vl ), and see the R2 and R3 resultant values.
The lower table allows you to set in the resistor values and it will calculate the upper and lower trigger points for you.
The Dynamic Solar Engine ( DSE ) uses a CdS photocell ( R5 ) to sample the ambient light level and set the upper and lower trigger voltages Vu and Vl to a level that is sustainable by the solar cells chosen for the Hornet. At higher values of R5, say 10,000 ohms in the example above, if you want to have your solar engine trigger at 5.0V and decay until 3.0V before charging is to begin again, you need to put in 16K and 17K resistors for R6 and R7
The lower spreadsheet calculation shows the opposite calculation. It solves the upper and lower voltage trigger point values, given the resistor ( R4, R5, &R6 ) values.
If you experiment with this calculation by entering R5 = 10,000 R6 = 16,000, & R8 = 18,000, you will find that the upper and lower trigger points come out to Vu=5.06V and Vl=2.99V.( Hysterisis = 2.07V ) This is a good combination for darker conditions where the value of R5 will be higher.
We can simulate a lighter ambient condition by reducing R5 to 6,000 ohms. You should see that Vu= 7.667V and Vl=4.217V ( Hysterisis = 3.45V! ), which is a higher voltage for the the upper trigger point and a much wider hysterisis for a bigger motor punch!
Now, the Hornet schematic only shows one resistor ( R5 ). The actual Hornet has the CdS photocell in series with other resistors to limit the maximum and minimum resistance to ideal conditions for activity at many light levels.
I hope this brief explanation serves to describe the operation of this cool solar engine. Please email us if you have any questions or if we have any errors in our description.