Re: Seeking circuit ideas....
- From: ehsjr <ehsjr@xxxxxxxxxxxxxxxx>
- Date: Wed, 20 Jul 2005 15:22:02 GMT
ehsjr wrote:
davidd31415 wrote:
Ehsjr,
Your understanding of my problem is correct. The relay idea sounds great, but I need a method to energize the relay. The joystick has 4 sets of outputs and when it is pushed in any of the "bad" two sets of outputs are activated simultaneously (there are not 4 separate sets of outputs, unfortunately). This is why I'm thinking the use of two relays may work, but I'm worried that fuses may still have time to blow before the relay opens, preventing the short. Perhaps slow blowing fuses and semiconductor switches will work ? I'm guessing normal mechanical relays will be too slow for this application.
Ok, so if I understand it, diagonal is indicated by one of the following combinations: N+E N+W S+E S+W
You can do that with 2 transistors, 2 resistors, and some diodes: +---[DIODE]---+ | | c---+----relay----+--- +Vcc South---[DIODE]---+---[R1]---b | e North---[DIODE]---+ | | | c East----[DIODE]---+---[R2]---b | e West----[DIODE]---+ | Gnd
R1 and R2 are 330 ohms. The transistors are PN2222A. The relay needs to be sized for the voltage (Vcc) and for the current that the motors will draw. The diodes are 1N400x. The banded end is on the right for each of the diodes above: --->|---
Ed
I left out the issue you so correctly raised about timing. That solution is simple, too. I'll draw the full schematic below. The circuit description follows.
---[Motor1output]---+
|
+------------+
| |
[Snubber] [RY1Contact] (normally closed)
| |
+------------+
| |
[Snubber] [RY2Contact] (normally open)
| |
+------------+
|
---[Motor2Output]---+
D5
+------>|-----+
| |
D1 c---+----[RY1]----+--- +Vcc
South--->|---+---[R1]---+-----b
| | e Q1
North--->|---+ [R4] |
D2 | | +-------------------------+
| | |
| | |
| +---Gnd |
D6 \ / | D8 |
----- | +----->|----+ |
| [R5] | | |
| | c---+---[RY2]---+--- +Vcc |
+---[R3]---+---b |
| | + e Q3 |
| [C1] | |
| | | |
----- +----+ |
D7 / \ | |
| Gnd |
| |
| |
D3 | c---------------------------+
East---->|---+---[R2]---+---b Q2
| | e
West---->|---+ [R6] |
D4 | |
+----+
|
GndC1 - 1uF, voltage rating at least 2x Vcc D1-D8 - 1N400x R1,R2, - 330 ohms R3 - 1K R4,R5 - 10K R6 - 47K Q1,Q2 - PN2222A Q3 - TIP120 Snubber - a capacitor in series with a resistor. Compute the cap value at 1uF per amp of motor current, and 3x motor voltage. Compute the resistor at 1 ohm per volt of motor voltage, and use a 1 watt resistor. These are rough numbers, so you can use anything near the computed values.
Diodes D1 and D2 form an OR gate. A plus on either South OR North will turn on Q1 via R1. R4 biases Q1 off in the absence of a plus on South or North. The same description applies to the second OR gate (East/West) and its components D3,D4,R2,R6 and Q2
The emitter of Q1 is fed by the collector of Q2. Therefore, both Q1 AND Q2 must be turned on for RY1 to be energized - an AND gate.
In English: Either North |OR| South |AND| either East |OR| West from the joystick is a diagonal. That's 2 ORs and one AND, just what is in the circuit.
RY1 - the "diagonal" relay, opens the offending jumper - the connection between Motoroutput1 and Motoroutput2 when it is energized, and it is energized any time the joystick is diagonal.
Diodes D6 and D7 form a third OR gate. If any (or all) of the inputs North, South, East or West is plus, Q3 will be turned on via R3, energizing RY2. The turn on of Q3 is delayed roughly 1 mS while C1 charges. R5 biases Q3 off in the absence of any input from the joystick, and discharges C1.
RY1 and RY2 form another AND gate. RY2 must be de-energized AND RY1 must be energized for the connection to exist between Motoroutput1 and Motoroutput2. It cannot exist until RY2 has transferred. It takes, as a rough average, about 8 mS for a relay to transfer. The closed contacts break long before the open contacts touch. So if we energize both RY1 and RY2 at the same time, RY1 will break the connection long before RY2 makes the connection. An additional delay is added to ensure that RY1 begins to energize before RY2.
The relay contacts are important. They must be capable of handling the current that the motors draw. If Vcc is 12 volts and the motors draw a lot of current, automotive power relays are a good choice for your relays. Something like RLY-443 from Allelectronics http://www.allelectronics.com/ will handle 40 amps.
Ed .
- References:
- Seeking circuit ideas....
- From: davidd31415
- Re: Seeking circuit ideas....
- From: ehsjr
- Re: Seeking circuit ideas....
- From: davidd31415
- Re: Seeking circuit ideas....
- From: ehsjr
- Seeking circuit ideas....
- Prev by Date: How to rust proof underwater alligator clips?...tia sal
- Next by Date: Re: How to rust proof underwater alligator clips?...tia sal
- Previous by thread: Re: Seeking circuit ideas....
- Next by thread: cheap pcb
- Index(es):
Relevant Pages
|
Loading
